Do you trust your farmers' market?

Spring marks the beginning of farmers' market season and I'll be checking out a bunch of markets throughout the Toronto. But a few friends have told me - without mentioning their source - they have doubts about these farmers, that they're truly local. According to some people, a few of these "farmers" are just trucking in good they got at the food depot near Toronto's waterfront, getting overseas produce and passing it off as local. Before I investigate this further, I wanted to see if anyone here had similar issues, if you knew about lying farmers at these markets. Every community is different, of course, but perhaps what is occurring in the States, say, might be replicated here. And do you go to farmers' markets often? What do you like about them?