I also say look for visible animals on the table ( they had to come from somewere), specially if the visible is same size. ask questions about the parents. as well as everything above. I found that my hets when I got them had the markers really heavy ( specially on the females) and the male had nice ones. always request something in writting and it should have 3 forums of contact
snail ( address) mail
a webpage/email
and a phone number.
I also see since most are bringing laptops o the show, about having a printed id for the snake so that noone tries to switch them laterand say sold me this snake as het and not proven 2 years later.. ( something I always liked ony my id papers)