The above two cases illustrate some of the deceitful practices that might be tried in commercial transactions. Even though there provisions might be made to prevent fraud – such as conduct of transactions in public, inspection of goods, third-party weighing facilities – a measure of trust and good faith was inherent in bargains, especially at a period before detailed record-keeping provided, if not a protection against fraud then at least more support for legal action. Both these cases suggest more than opportunistic fraud; they suggest experienced con-men knowledgeable in manipulating trusting and unwary clients.

Indeed, Roger Aldith had already, on more than one occasion, run afoul of the Leicester authorities for fraudulent practices in his cloth business, as well as for insulting the mayor and the provost of Leicester. So incorrigible was he that he had been expelled from the merchant gild, only to repurchase admission upon a solemn promise not to offend again, upon perpetual loss of membership and a hefty fine. It must have been galling for his fellow Leicester merchants then in Lynn – if such are implied by the "good men" – to have to help him out of a difficulty clearly of his own making. That he survived this further disgrace is indicated by the fact he was a contributor towards community tallages in 1269 and 1270.

Raw wool was the most important commodity exported from medieval England, and might be seen as the oil of the Middle Ages, for it fuelled the cloth-making industries of continental Europe – particularly Flanders (first and foremost), northern France, and northern Italy – though we can only take this analogy so far. Most cloth, apart from the silks that were a luxury product, was made from wool, though some from hemp or flax (canvas, linen). Top-grade English wool was the best in Europe, with Spanish wool unable to match it until the sixteenth century. Its trade was probably already a foundation stone of the English economy by the eleventh century, and by the late Middle Ages almost every large town in England, and across Europe, had a local textile industry, so that English wool could almost always be sold for a good profit, particularly abroad (notwithstanding the overhead of taxes, packing, and shipping).

Many English merchants therefore dealt in wool to some extent. Some, who had developed connections with small producers or had built up knowledge of when and where farmers would market their wool, and having assembled funding (sometimes by partnering with one or more investors), would make periodic circuits of rural markets and sheep-farms, aiming to snap up wool supplies before their competitors could. This strategic knowledge needed to be protected. In February 1260 Leicester's merchant gild enacted various rules regarding their members' participation in the wool trade, including that "no-one who belongs to the gild is to travel through the countryside in the company of outsider merchants, instructing or helping them in the purchase of merchandize, to the detriment of the gild." [Bateson, vol.1, p.92, my translation.]. Offenders would lose their gild membership, while non-gildsmen convicted of the offence were to be exiled from town for a year.

The story of the wool trade in the medieval period is often portrayed as one of gradual but growing monopolization by English middlemen and merchants – thanks in part to royal taxation of foreign exporters and the development of the staple system to favour English exporters – and of increasing channelling of English wool into domestic cloth-making. By the fifteenth century wool had been exceeded by English-made cloth as the major export, although the two together made up more than 90% of England's total earnings from the export business.

Wool was produced from flocks raised on the vast estates of lay and ecclesiastical land-owners, as well as on large numbers of smaller farms generating much smaller quantities. The great estate owners, particularly monastic houses, tended to contract out in advance the sale of annual wool crops to some mercantile exporter, or his agent – an arrangement that was (at least on the surface) less troublesome to the houses, even though they might make less than market price, and more profitable to the agents – who could sell wholesale at fairs or ports, or export and still make a good profit – or at a later period to merchants coordinating industrial cloth production. The crops of the numerous small farms had to be collected by the landlords of the farmers, agents of exporters, or other middlemen, some of whom were professional enough to be described as woolmongers or woolmen. These middlemen tended to be based in the regions where they collected, although some might come from as far afield as London. Some were drawn into exporting in their own right.

Wool was generally bought and sold wholesale by the sack, although smaller quantities such as the nail, or clove (52 to the sack), or the stone were also used. A 'sack' was a weight, however, rather than the container of the wool; the container in which wool was baled was the sarpler, a cloth usually of sturdy hemp or canvas; containers smaller than a sarpler were known as pokes and pockets. These terms were applied both to the cloth packaging and the entire container when filled with wool. The middlemen who bought wool from its producers (i.e. owners of flocks of sheep) would put it into storage until it was time to take it to a fair or until their own premises were visited by merchants who would export the wool. The wool was usually stored loose, with packaging into bales taking place after a sale, but being the responsibility of the middleman prior to exporting it; by the fifteenth century it was required that wool be packed in the county in which sold, and the packaging was an important part of the mercantile process, undertaken by officials or with official supervision, and with the middleman or his agent present. By that period it required about 12 ells of cloth (usually canvas), sewed up, to form a sarpler into which wool would be compressed; the cost of this cloth, which was mostly imported, had to be factored into the sale price of the wool. The amount of wool put into a sarpler varied between the thirteenth and fifteenth centuries, ranging from half a sack in the earlier period to two sacks or more in the later.

Purchasers would of course want to inspect the wool, to assure themselves of its quality, before placing an order for a certain weight (in sacks) or number of sarplers. The quality of wool varied depending on the region where the sheep were raised, and the age of the wool, and how fine or coarse it was; some of it was considered too poor to use for cloth-making, and contracts sometimes specified that sellers should remove such refuse wool. This variation in quality is reflected in the document above in the two different prices William de Dunstapele was to pay for two different grades of wool he was buying.

By Late Middle Ages it was becoming common for exporters to supervise the packing, in person or by agent, and have each bale marked as to the quality of wool therein and its source region; one fraudulent practice was for merchants to alter the markings to make it appear the wool was higher quality than was the case. The purchaser's merchant-mark would also be applied to bales acquired, and customs collectors came to be expected to record the names of the merchants whose wool was exported. Another fraud was to try to pad wool of one quality with wool of a lesser, as the document above exemplifies, or even to adulterate it with other materials to increase the weight of a sarpler. Weighing, by officials stationed at ports, would take place before sarplers were shipped, and again before being sold at their destination.

With the weight thus determined through a third party, much of the bargaining involved the sale and purchase of wool revolved around its quality; A letter of 1480 from George Cely, acting as the family agent at Calais to receive at the staple there, and to sell at the fairs of the region, family wool, reports back to his father Richard on aspects of the bargaining by one of the family's regular customers:

"He swears to me largely that he has had of yours in time past better middle young Cots. than this wool was. They lay unto me great unkindness that I deal with them under this manner. They say unto me that ye might 'an taken out of this 6 sarplers and the poke, 2 sarplers middle young.... I had much work at Calais ever I could have awarded it for Cots,, and much sticking was against it amongst the Fellowship [of the Staple]. In the reverence of God, see better to the packing of your wool that shall come, or else your wool is like to lose that name that it has had ever affore in time past. I never wist you send coarser wool to Calais for the country than this last was."
[Quoted in Alison Hanham, The Celys and their world: An English merchant family of the fifteenth century, Cambridge University Press, 1985, p.117]

Cloth was a product needed by everyone, rich or poor, and so its manufacture was the driving industry of medieval Europe – particularly in the pre-plague centuries when the population was expanding – with constant effort to improve quality and reduce costs, such as by making lighter, yet still durable, materials that were cheaper to transport, or alternatively to produce cloth such as worsted affordable by the lower-classes for daily wear, if not as long-lasting. Because cloth-making, on a scale other than for household use, was an industry that involved numerous specialized workers in different stages of production, it was natural for it to develop in an urban setting, where the size of population made occupational diversity practicable. During the first half of the twelfth century we see weavers organizing themselves to some degree in a number of the larger towns, such as Lincoln, Winchester, and London; by the close of the century cloth production was an established industry in many towns. Expansion of English involvement in international trade – even though England's raw materials were for some time more important than its manufactured goods – was a boost to the industry, even though English cloth was of a lower quality than that produced in Flanders or Italy (despite workers there relying partly on English wool); whereas, by contrast, the great cities of northern Italy imported quantities of raw materials (for industry and for feeding workers) in order to support its larger-scale industrial productivity.

The growth of the network of fairs in England made it easier for Flemish cloth, imported and distributed by Fleming merchants, to penetrate the English market. But gradually cheaper access to high-quality English wool enabled the domestic cloth industry to become a major source of decent quality woollen textiles, although the export of this was initially dominated by Hanse merchants and other foreigners. Increasing royal taxation of foreigners' exports helped bring more English merchants into a competitive status in this trade. But factors such as urban over-regulation, cheaper rural labour costs, use of country watercourses to power fulling-mills, and the rise of entrepreneurs who could, with very little capital investment, coordinate the various decentralized phases of production, encouraged migration of the English cloth-making industry into the countryside or to smaller market towns (most famously, Lavenham), though these producers did not predominate until the close of the fifteenth century. Prior to that the established urban industry might, in some towns, be weakened by developments, but was not entirely displaced, while in other towns it was not even seriously threatened. In the fourteenth century the cloth industry in Flanders itself suffered from political disturbances, providing greater opportunities for English merchants in both domestic and foreign markets. It has been said that "The most striking characteristic of England's overseas trade in the fourteenth century is the decline of raw wool exports and the steady climb of the export trade in cloth." [Colin Platt, The English Medieval Town, London: Secker & Warburg, 1976. p.88] The competitive production cost of English cloth was, however, offset by rising costs related to distribution (e.g. transportation, and measures to try to exclude English cloth from some European markets), and by continued preference among wealthier customers for the luxury and high-quality textiles of continental producers.