Sounds like a space cadet.
He could set up a Fixed Price listing for you at the agreed price plus shipping.
He could use your name as the title and give you a deadline for purchase.
Both of you would then be covered by eBay and Paypal Protection policies.
However, you should be aware that eBay frowns on buyers making offers to sellers who have not purchased the Best Offer option. Buyers can be reported to eBay for such pesky moves.
Basically, he is not too interested in your offer. Move on.