Sale of goods in open markets was seen as a means of ensuring fair trading – the goods were in clear sight, they could be investigated, but there were many scams to cheat this system. I have read of butter being sold that had a core of lard with only a surface of butter around it, but for many years, weights and measures were local, so varied immensely until a national standard was established. One of the most important duties of market officers was therefore to ensure correct weights and measures were used by traders, and to punish those who cheated. This is from the Leeds Intelligencer of April 1765
We hear from Richmond, in this County, that the scandalous Perseverance of some People in that Town, in using fraudulent weights and measures, had induced their late worthy Mayor to appoint a jury to suppress such infamous practices. Accordingly, (with the assistance of the Recorder) they have exerted themselves greatly on the occasion; having on the 6th inst. caused to be publickly burnt at the Cross, at High market, six yard measures, eighteen pecks and half pecks, and several lesser measures, with one venerable bushel gracing the pile; a great number of weights, of different sorts, were also broke and melted down.