I would take him back to the breeder and ask the breeder to have a look at him. If he had a 16 foot table at a show covered in snakes, he probably knows a thing or two about them and can help you figure out what's wrong with the boa and help you set him up properly, but there is something wrong. Don't stop until you find out what it is.

He's a very pretty snake - it'd be a shame for him to become permanently damaged or destroyed by you taking solace in some useless vet's obviously skewed opinion. Pursue the issue. If you decide not to, bring him to me, lol, i'm in boston. I'll trade you a real, healthy male ball for him.