See if he wants to use a escrow service for payment. https://www.escrow.com/index.asp
You give the money to the escrow, if the bike is not shipped, they dont get the money, they wont get the money until you say everything is as said.
If he doesnt want to use escrow, then its a scam for sure, if he has no problem using escrow this just may be a legit offer. If it turns out to be a fraud, then you can warn people of it.
I personally would rather not buy a bike overseas, I like to be able to look at and test drive anything I buy before I turn money over.