Such cases happen. You must always be careful.

I think Tavenger is right. If you are in doubt, then I would get the ESN off the Ebay listing and call the provider. There are also plenty of websites where you can check the ESN. If it comes out clean, then maybe contact the seller and have them release it from their account.

It sounds like the person who sold it forgot to deactivate it. So more than likely the ESN is clean. The seller just needs to release it from their account. Where the actual number is from isn't relevant so much anymore.

I'm too cheap to buy anything new... and since everyone in my family abuses phones ( phones here are known to go swimming, committing suicide off the table onto a concrete floor, and laying down in front of a car to be driven over) I get used ones... I learned the whole clean ESN thing.. and crossed my fingers when the phone arrived hoping it was as good as promised... so far so good... every phone has preformed very well before someone ended it's career as a talking device and demoted it to a paper weight.
With that said... a friend's phone was on it's way out... I happened to be trolling through ebay at the time of our conversation and on a whim I bought her a phone.. under 20 bucks and I wanted to do something nice for her... problem is.. I didn't confirm if it has a clean esn.. I got all caught up on trying to outbid someone at the very last second.. She has boost mobile ( I managed to get that right) and when I sent it down to her ( she lives in Florida and I in Ohio) she received it.. turned it on and could make phone calls and get online... with out activating it... she looked and found that it has a month of minutes on it... those minutes were added after it left my house while in the mail...
Now.. short story long... did I purchase a stolen phone? if I did.. why on earth would someone add minutes to a phone they don't even have? do I just pretend nothing happened since it was unactivated when it left my house?
Btw... the buyer said he was from Florida... the phone shipped from Washington... and it has a Georgia number...