I don't know why farmers markets are given such a benefit of trust. They are largely unregulated and uninspected. And you'll pay $8 for a head of lettuce.
This is why I only buy from the farms I know and trust. There's two families I know who sell at smaller markets in the city and one farm that is close enough to my house I go directly to their farm where they have a small setup where a lot of other locals go.
You're right though there are a lot of unsavory people who claim to be from local farms but very clearly are not. People who are selling sweet corn in May/June claiming their local. Sweet corn isn't normally harvested until late Summer, early Fall.