I think blaming craigslist or any other way of purchasing a snake is excusing the purchaser from much of the responsibility. I don't care if you buy off craigslist, a pet store, some breeder you've never heard of at your local snake show - if you aren't doing your homework before getting the snake, you are going to at some point get ripped off or end up with a mess on your hands.
Know what a healthy snake of that species should look like, ask specific questions about this snake's history, get info on feeding habits and feeding history, learn the red flags that might indicate a problem with the snake or the person selling it, research breeders, learn to sex a snake, get a contact number from the seller in case of problems, etc. Not doing any of this first before putting down your hard earned money then blaming the seller, well hate to say it but you have set yourself up. Sellers should sell healthy snakes and be honest about stuff but buyers have to be responsible too for their half of any transaction.