I would rather the government do their job and police and prosecute illegal acts.
People selling bikes include both first-hand buyers and second-hand buyers (people who bought it from someone else).
Without a central registry like what we have for cars, I don't know what Facebook could do.
Is there a possible way for FB and other similar places (offerup, pawn shops, etc.) to verify without some central registry?
Also the legislature could make laws to make it easier to send bike thieves to jail.
The government != Facebook and it's better that way since we can vote to change things that we find wrong with the government, but lack that ability with FB