Since you don't know who will be vending, once you find a critter you like but before you put down any money, find the vendor's name and look for reviews here:
http://www.faunaclassifieds.com/foru...splay.php?f=13
There are some vendors who are great and sell healthy, quality animals. There are others who will happily take your money and hand over a slithering vet bill.