I assume you are buying used, from an unknown third party.
Found this, it might work for you.
A word of caution when checking ESNs. Be sure you see the numbers for the phone you are buying with your own eyes when confirming. If the ESN comes out good and you decide to buy the phone, be sure to recheck the ESN on the phone before you hand over the cash to be sure the phone has not been switched with one that might possibly have a bad number.
Never accept a ESN number on a phone/potential purchase from a unknown party as correct. These shysters are aware that people are catching on to their trick about selling phones with banned ESNs. Buyers pays hundreds for a phone and the seller walks with the money. Customer is now stuck with a phone that can never be activated.
If the seller will not let you see the numbers with your own eyes or lives out of town/state where it is not possible to see them I do not recommend buying.
People lie cheat and steal on Craigslist and EBay all the time in selling bad phones. Another forum has people crying for help all the time because they got scammed on one of these sights.
Ebay will fix a sale gone bad and go after the seller, Craigslist will not.
Just remember if you can not confirm the ESN before the purchase and then again at the time of the purchase. DO NOT BUY.