I know a lot can be, but not all pet stores are evil. Yes it is true that they probably don't want you going directly to the breeder and cutting them out (or maybe the breeder does not want 1000 phone calls about stuff they don't even have anymore, I know some like this), but they are trying to make a living, it does not mean anything is wrong with the snake. I did see one just posted on facebook for $500 (plus shipping, generally around $50), a male lesser/mojo BEL. Not sure on the weight of either snake (larger is typically more $$)

if you like the snake and the price is not horrible and you don't want to wait or mess with other sources, why not?
I'd just make SURE that it is eating, and what it is eating, and when it last ate. (and get the enclosure set up first, they will generally hold it if you pay for it, so you can get everything setup first)

they do look cool. I just got some eggs from my Mojave female, hopefully I'll have some baby BEL's in about 50 days!