Absolutely true! That’s why I advocate talking to farmers at the markets! Ask them where their farm is located, what their growing practices are - in my experience, the good ones love to talk about that stuff. The ones that are hiding the fact that they went to the local commercial produce supplier and grabbed whatever veggies were cheapest and brought them to the farmers market will not.
The town I live in has a 60 year+ history of city-managed farmers markets. They include their farm names and history right on their signs, and while I know many places do not have this option, I still strongly believe the best thing you can do when choosing the food you are going to eat is to talk to the producers you are buying from, you will find farmers at the market that care about growing good, sustainable food and are happy to tell you about it. 
This stuff matters to me (as I’m sure folks can tell), as I have a proud history of local, small-crop farmers in my family, who work hard to make good food, because they eat it, too, and so do their friends and family, and they want to leave their children sustainable land that they can continue the tradition of farming on.
