Talk to the people you might be buying a snake from as well. You will be more comfortable making a purchase, especially if it's online, if you've established some form of dialogue with the seller.
x's 10! i agree! building a good foundation/ communicative relationship with your seller will give you a good informational asset.

the best advice given on this thread though, is know what you need and get it all set up & running BEFORE bringing a new snake home.
also i dont know the adult length of corns but i'm almost positive they stay on the very small side am i right? bp's can get up to 4 1/2 - 5 ft, so you really need to know for sure that you can provide an adequate home for something of that size? granted these snakes like somewhat cramped spaces but even still i'm sure they'd need a home a bit bigger then that for a corn.