Fleming Reptiles is gonna be at the Atlanta show and they sell Boas, I couldn't find anything bad on the BOI on them. Just inspect your potential new pet. Feel the body for lumps and things like that, check the mouth for bubbles and because it's usually loud as heck at these thing you probably won't be able to hear wheezing or anything like that but check anyway. Look at the eyes and nose they should be free from debris and such.
Check the snakes behavior, it's a scary place for a reptile it shouldn't be listless it should be alert and flicking it's tongue all over.
If if you are curious about a particular breeder the. Just ask someone who isn't competing with them. So ask the guy with the table full of frogs or leopard geckos maybe buy a hide or something and see if they've heard any bad things about a particular breeder.