I have seen plenty of unhealthy babies, of all species. Just because they are babies doesn't mean they are being taken care of.
If I were to buy an animal on craigslist, I'd ask for pictures, multiple pictures, including the enclosure it's being kept in so you have an idea if it's being cared for correctly. I'd personally ask to meet at their house so I can see if any other reptiles were sick, but I know most people don't do that. Check for mites once you have it in hand. I'd be sure it's eaten a few times too. And I'd also have a fecal test done after it's first defecation with me. Call me paranoid, but a cheap reptile isn't worth my whole collection....