Oh yes, my friend, oh yes. There was all the fraud you could want (or rather, not want). I'm going to talk about food fraud, spice fraud, wine fraud, clothing fraud, and alternative medicine that was a little too alternative.

I'm going to talk primarily about markets in late medieval Europe, which means we're talking pretty much about shoppers from a range of social classes and payments in money.

Bread was the basic food of late medieval cities, especially poor people (the city residents we never think about). Some cities even had laws mandating that no matter the price of various grains, bakers were required to sell their cheapest loaf at (the equivalent of) half a penny. So selling bad bread was particularly common and particularly harmful.

One popular cheat was to sell loaves that weighed less than claimed. Since there was a hierarchy of prestige in terms of grain used, mixing a little (say) barley with oat flour could yield the seller a bit of extra money.

...and then, of course, there was the mixing in of things that were in no way flour. Cobwebs, dirt...A particularly "enterprising" baker might even combine frauds. Run out of cobwebs? Running really short on flour? Mix some (presumably small) stones into your loaves, so they'll meet the weight requirement, too.

There was also the sale of rotten meat, or meat that had not sold the previous day, but clearly we can get more creative than that. The medieval equivalent of the McDonald's hamburger was a personal-ish pie--specifically, a pie with a bottom crust, a top crust, and a big space in between that was not visible during sale. We have records of sellers putting in rotten meat, kitchen scraps, no meat.

Barbara Hanawalt cites the 1351 case of London pasteler Henry de Passelewe ("de" was common in medieval English surnames) to demonstrate how the process of catching pie fraud might unfold. One customer, ravenous, bought two pies. With the help of a couple of friends, he ate through nearly an entire pie before realizing the meat was rotten. So was the meat in the second. The customer took the two pies to city officials, who further called in two pastelers to judge. The meat was indeed declared rotten. (I don't know how long this process took.)

Punishments for selling bad bread and meat were based on public shaming. Time in the pillory was common; the other major element was to be paraded through the streets with the illegal merchandise dangling from their neck.

Selling fraudulent spices, one imagines, was one of the easier schemes to pull off. Spices constituted, for the most part, rather expensive dried powders that were claimed to come from "the East", and could act as flavorings or medicines. We're talking everything from cinnamon to tutti from particular origins (which meant, usually, chimney scrapings). So it had to have been reasonably common for apothecaries and others to turn some extra profit here.

Drinks with alcohol in them--wine, beer, ale--were another marker of social and monetary prestige, both in terms of their quality and in terms of being simply not water (the drink of the poor). The geographic area of land in Germany that produced wine was far larger than today, but the wine was less than ideal. So German cities had laws against selling German-origin wine as Spanish or French. To water down one's wine was another pretty obvious trick.

One Middle English satirical poem by John Skelton, The Tunnyng of Elynor Rummyng), has very much fun describing a particular type of ale fraud:

And sometimes she blends

The shit of her hens

And the ale together,

And says, "My friends, come hither!

This ale will be thicker

And flow the more quicker."

(And, Skelton describes, even when she doesn't blend it on purpose, her chickens defecate in the vat of ale and she just shrugs it all away.)

(Also--most of the point of the poem--EVERYONE LOVES THIS ALE. One person even trades their wedding ring for some...)

Clothing fraud--mostly what I've read about in this realm is clothing sold as being made of new cloth was actually made of secondhand cloth. And this wasn't just at the buyers' end. In Rouen, members of the guild of drapers of new cloth sued the used-cloth drapers' guild for honing in on their territory.

And that brings us to alternative medicine that was a little too alternative. The modern opinion of medieval medicine tends to be, essentially, "Ummm..." But in fact, quacks had a very large presence even as elements of medieval popular culture. Selling cures for diseases that did not exist, or attempting to make people sick in order to cure them, are good examples here.

But there was standard lying about what would work (that is, in the minds of medieval people). This might be harder to prove straight-up, so cities had to find other ways of dealing with it. In late medieval Italy, cities tried to restrict sellers of snakebite-cure to the outskirts of the city, or even outside the city walls.

That is, the snakebite-cure sellers who marketed their wares with giant flags and, well, with venomous snakes.