After much thought, I'm leaning towards keeping the phone because 1) If I send it back to the seller, who's to say I won't see any possible charges on my bill later even if I don't have insurance? That would leave me with NO phone and charges on my bill.
2) He already has my name and shipping address, so who knows what else he can pull AFTER I return the phone since someone has access to a sprint customer database and they are already involved in such dirty practices?