Clean ESN and icloud activation (as mentioned by Lisa) need to be checked.
Clean ESN means your carrier can accept it is not stolen and blacklist phone, to check this you need the IMEI number from seller and use swappa and iphone.info to double check the ESN.
Next step make sure activation code is unlocked.
Bought it. Checked out the Blacklist for Canada, iphone.info and Apple's SN and it all checked out fine. Has Applecare til mid May 2015. My son will be happy to get it!
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