We know of farmers who go to cattle auctions and buy the cheapest steers they can find -- often sick and/or emaciated ones coming from farms in financial distress -- then fatten them up on grain while giving them pasture to forage, and sell it as grass-fed at farmer's markets. Just install a pretty girl in a tank top and a Realtree baseball cap at your booth and it all goes off without a hitch.
A good rule of thumb is that 1 acre of grass supports 1 head of herd. When you go to the farmer's market, ask the people selling you beef what their herd size is and how many acres they have under pasture. They should know these numbers cold. They should be ready to talk your ear off about how much of a pain in the ass haying is. They should know how calving is going and how many calves they've lost this year.
It is very possible, easy in fact, to raise animals (or vegetables) in toxic conditions and turn around and sell into farmers' markets. If you want clean food the answer is simple; buy into CSAs with farms run by people you trust. They should be willing to let you come to the farm, walk around, ask questions. Many of the best farms are not certified organic because they smartly use stuff like potash that is cheaper, makes better vegetables, and ecologically way better than organic equivalents when used in the right amounts.
I find it interesting that much of the discussion on this thread has centered on enforced standards. There has never been good enforcement of governmentally-sanctioned standards pertaining to high quality farm produce in the US. Certain private organizations are OK but the people administering them tend to be assholes so that results in a lot of farms (including ours) doing things the right way and selling to people who trust us, without getting formal certification.