12th Century Fairs
In large cities some markets operated every day (for example the wine market in London), some fresh produce could be bought daily from market stalls, fresh cooked pastries could be bought from wandering sellers, and a wide selection of fresh uncooked food could be bought from the large farmers market once or twice a week. Once a week or month (depending upon the city) other goods (e.g. shoes) might be sold in an open air market. Craftsmen owning shops would close their shops for the day to sell goods from a market stall.
Fairs were big events held in large squares in cities, or more often in the fields surrounding the city. Fairs were generally annual events, lasting about a month, where traders travelled long distances to bring luxury goods to sell, and many people from smaller towns might make their yearly trip into town while the fair was open, to sell their produce (e.g. livestock) or pick up special items (e.g. finely woven cloth). Fairs were great for the economy of the town that hosted them - think of the effect large SCA camping events have on the nearby towns with sales of food and accomodation. There was a lot of competition between towns to get a reputation as the best fair, thus attracting better traders and patrons.