I don't advocate buying from pet chain stores, either. Still, I'll have to play devil's advocate a bit. My kids and husband bought my first corn as a birthday gift for me from the local PetSmart, along with frozen pinkies to feed her. She's a basic amel, nothing fancy, but quite healthy and growing fast. I do believe that she'd been underfed a bit, based upon her strike response with her first feeding at my house. Still, she's a great snake and I'm tickled to have her.
My next 4 came from Kathy Love, purchased online. No problems whatsoever!
There are 3 mom and pop pet shops near me that handle herps. One is clueless about morphs but tries to take good care of their reptiles. She occasionally has a surprise goody. One is pretty knowledgable and loves corns. The other, while claiming to specialilze in reptiles, I avoid because it's too depressing to see the conditions in which they keep their animals.
So, while I definitely agree that buying from a breeder is far and away the best choice, it is possible to get a healthy snake from a chain store. Just be prepared to pay more than from a breeder, and be aware of what to look for health-wise.
BTW, there aren't any regular shows/expos near me. I'm going to Pensacola at the beginning of August, but I really envy you folks with monthly expos!