The number of farmers markets in the United States has gone up almost sixfold in the last fifteen years. Whether they started out as a consolidation of honor-system fruit stands or as a place for farmers to sell produce that was too ripe to go through the food distribution system, they've established themselves firmly in the American produce landscape (though they represent only a tiny fraction of the produce bought and consumed in the United States).
But what makes a farmers market a farmers market?
Here in California, the state certifies farmers markets. In order to be certified, a market must contain only produce grown by the people selling it, though this only applies to produce, not baked goods, crafts, etc. After the scandal revealed by KNBC-TV Channel 4 late last year, where vendors at the Buena Park farmers market were shown to be lying about the origin of their produce, certified farmers market managers are more vigilant than ever about their vendors.
Stores with “farmers market” in their names, such as Sprouts and Henry's, etc. are not farmers markets in any sense. They're simply using the term to conjure images of farm stands and real farmers markets. If you've ever bought, say, broccoli from the Village at Orange Certified Farmers Market (on Thursdays) and then gone into the adjacent Sprouts and bought broccoli, there's no comparison.
Unfortunately, there's no restriction on using the term “farmers market,” either as a noun or as an adjective, and so grocery stores are free to advertise “farmers market plums” even when the plums in question came from the produce warehouses in central Los Angeles and have PLU stickers attached to them.
Does this mean that a collection of tents selling produce in a parking lot that is not a certified farmers market is necessarily bad? No. Companies may want to bring in fresh produce and sell it in their parking lots, but that doesn't make it a certified market. It's worthwhile looking, as long as there's someone available to answer questions–and answers to low-level questions such as the type of pest control used may not be known.