this guy sounds like a scammer....you can tell by the fact that he is willing to pay more so you send the item out early. Any genuine bidder would not be as persistant as he has in terms of payment if they knew that the payment was legit.
The fact that you have refunded him the money and given him another opportunity to pay using a bank transfer would mean that he would pay if he really wanted the item. If he claims to have paid it would show up within 3 working days or sooner. If the money does not appear in your account by Tuesday at the very latest relist the item.