1) Ask to see the bike, if he is in one category of scammers, it wont be available for inspection, a whole variety of good excuses why, just went in the military, moved because of job, etc., he will want to use something that he says is Ebay Escrow services through Western Union bla, bla. Run fast and flag the ad, this is typically a scammer from Africa.
2) If you can see it in person, do so and get the VIN and see if the police will run it for you--but even if that is clear, it could have liens on the title thus see if you can get the State bureau that handles license plate issuance to run the VIN.
3) Run a VIN check for $3.50 at
Check that VIN! Used car title history search from CARCO Group and NMVTIS as this should discover salvage and problem titles but will not disclose liens or stolen vehicles.
3) In many states, if a vehicle is 6 or more years old, you can file an application to get the title, generally a simple procedure.
4) Run his phone number in Google and you will see several craigslist ads pop-up, one of his previous ads for the same bike had been "flagged" --never a good sign. I tried calling his phone number and got an automated message that the "subscriber is unable to receive calls at this time." Maybe he just didn't pay his cell bill..
5) Don't loose sight of what the Post Office warns,
"if it sounds too good to be true, it probably is."
Thus endeth the lesson.