Haymarket is overwhelming and worth the craziness. Bring a big bag for your groceries so you can better navigate the crowds (and the T ride home). Walk through the entire market before buying anything; often prices will be higher close to the front. Come early if you're buying fish. Also, prices are higher earlier in the day, but if you come after 3 you can get incredible deals on entire flats of things - sellers will practically force them on you as they can't sell them the next day. Go through everything once you're home and pick out anything rotten, so you don't spoil all of it. Also be aware that indecision is frowned upon, and if you try to buy one of anything - say, a single peach - you will be laughed right out of there. Just buy the three for a dollar and say thanks. You're getting a deal. And if a seller is rude to you, just move on - they have competition.