Don't give him the entire serial number,,,
SN: 123456,,,
Give him: 123XXX or 1234XX
It may be an urban legend but there is the tale of someone giving out a serial number,,,
Then the person turned that number in to the police as a stolen weapon.
Personally I wouldn't take the chance,,,
A partial number will allow him to identify it to the manufacturer.
JMHO
Aarond