I've bought a couple from Craigslist with OKish results. First one I bought, the guy was actually the one that produced the snake and knew the hets, what it was feeding on, and was very informative. He's not a large production breeder. I've seen him once since when we were both working a repticon.
My second experience the owners barely knew anything about their snake. They had him over 2 years, in an enclosure way to big for him, no heat at all provided, and was still feeding him the same thing as when they bought him (a fuzzy mouse). He didn't even have a name, they just called him "the snake". His tank was clean and well kept but very clueless owners. He's been a great little guy.
I hate inquiring about an ad that is older and the seller gets pissy that you are inquiring about it because "that snake sold along time ago". Well take your ad down if it sold and you don't want people still contacting you.