Worked in a bikeshop part time for 5 years, would happen all the TIME! eg; shady guy would come in with a flat tyre- the bike is a $2000 complete custom bmx which we happened to sell to the original owner, we say we'll fit the tube for free.. once the bike is behind the counter we say how kindhearted he must be bringing in other peoples bikes when they get a puncture. I have secret markings on all my stuff incase it ever happens to me.