HOw i can tell if the ESN on sprint phone is cleared or clean?

im asking this question because i just recently bought couple of sprint phone that people owned them Befro and im trying to resell those phone but i don't want to sell them if the have not cleared yet ?HOw i can tell if the ESN on sprint phone is cleared or clean?
You can just call customer care and they will tell you if they are on the negative file. Their number is 800-639-6111HOw i can tell if the ESN on sprint phone is cleared or clean?
Most ESN numbers and MEID's actually clear and are ready to be re-used on 2 to 3 months, now if you want to sell the phones so that they can be flashed over to another company that uses CDMA phones there will be no problem you can just sell them out without having to wait for the ESN to be cleared up.