Originally Posted by
katsup
I wouldn't give a seller the serial number. They could register it under their name, report it stolen and you'd be stuck proving it's yours or be forced to hand over the bike.
In person, I don't mind them checking.
Which is why I register my bike serial number when I purchase it and keep my sales slip.
The idea is that if you ask for the number to check with local PD, and the seller knows the bike is stolen, they will hang up faster than if you were calling about their car's extended warranty.
The other option is to tell them you'll meet at a safe place, like the parking lot at the local police station, and while you're there checking over the bike, they can run the serial number.