...keep him busy with BS questions and promises. Be sure to tell him the money is on the way, you can jack with him for days on that and it really pisses them off.
Once I had a guy from Nigeria contact me about a DD I had bid on on eBay (back when bidder info was visible). he said he had the exact same watch for half the price. It was an early pink gold 6611 so I doubted very much that he did.
I decided to mess with him so I wrote back and told him I was opening a watch shop and had 250,000 to spend in inventory and could he help me find enough vintage Rolex to spend that much money.
He blistered the ethernet to inform me I had come to the right place and he could certainly help me spend all that money. Thus began a long exchange of lies on both sides and finally when I could sense he was losing patience with me I decided to deliver the coup de grace.
I wrote him and apologized for wasting his time but that I had been in concurrent communication with another Nigerian vintage Rolex dealer there in Lagos and and that dealer had said he could get me the same watches for 200K so I had just wired the money to this other dealer and was waiting for my watches to arrive.
My "dealer" went insane. He demanded to know who this other dealer was, he guaranteed me I was going to be screwed out of my money, that HE was the only person in Lagos I should be sending my money to, he said I must pull the wire back immediately and that he would sell me the watches for 150K because of our long, friendly exchange of mails, yada, yada, yada.
His pain at losing this huge amount of money was palpable. Cruel you say? This man would have taken my last cent and left me destitute on the street if he had been able to, that's what thieves do.
So gentlemen, play with our young thief as long and as often as you can, you might save some other collector from this scum by wasting his time...and it's fun!