First, it's important for the ecoconscious consumer to understand that there are two types of market models, and one is anything but a true farmer's market. In some venues that resemble farmer's markets—and perhaps present themselves as such—buyers resell produce they bought wholesale. While this market may have a "local" feel, the produce may have been shipped in from faraway states or other countries. If it's from outside the U.S., it may have been harvested in socially unjust working conditions, or may contain toxic pesticides banned for use in this country. (All of which are things that many farmer's market shoppers are specifically trying to avoid.)
More: How to Make the Most of Your Farmer's Market
Conversely, in a producer-only farmer's market, the farmers at the market actually grow the food that they're selling, explains Bill Duesing, president of the Northeast Organic Farming Association. (Exception: Some state- and market-specific rules allow some farmers to sell a small amount of product from another farmer, or produce grown out of state, or baked goods containing ingredients that are not local.) If a market doesn't explicitly identify itself as producer-only, you can find out by asking the sellers. "The local question is an easy one," explains Duesing. "Ask the vendor, 'Where was the food grown,' or, 'Did you grow this?'"