Honestly, for inexperienced keepers, Craigslist is probably not the best place to buy an animal. Sure, there can be some great deals, but in my opinion the risk doesn't outweigh the reward.
Snakes are fantastic at hiding illness, and for a new keeper it would be even harder to identify possible health problems. If the animal does have any illness you'll end up putting your other snake at risk, spending a lot more than $60 on vet bills, etc...
You're better off buying from a reputable breeder. It's just safer and smarter.
The possible het is a crapshoot where you're putting your trust in the seller...I wouldn't trust a stranger. And the het only matters if you're breeding.
If you do go that route, make sure to quarantine very strictly for at least 90 days. You definitely don't want to put your other snake at risk.
If you're not familiar with the quarantine process please study it and follow it to a T. New feeding equipment, changing clothes and washing after doing anything in the QT room (which needs to be a completely separate room from your other snake), etc...etc...
...and there's no need to jump at the first opportunity to pop up either. There will be others...