I thought I'd start this based on another discussion and just that I see a lot of confusion as to what constitutes a farmers' market.
Since a lot of people don't seem to know what grows in their area and when, they don't realize the difference between an actual FM and a market that simply uses that as a name. I've seen complaints of markets not having as much selection as others because one actually sells local produce, so if it's early spring, for example, there isn't going to be much available compared to the market that isn't actually selling local produce.
So, when a market is selling sweet corn and peaches here in early May, that's not an actual farmers market associated with Grow NYC. Likewise if you live in Minnesota and you go to a "farmers market" that sells you mangoes or avocados at any time of year, you're not getting local produce.
Some people will buy produce in bulk then turn around and re-sell it to unsuspecting consumers who think they're supporting the farmers.
More useful info here:
http://farmersmarketcoalition.org/joinus/faq