Given the domain (a highly surveilled city, drivers making documented stops, a high standard of evidence) there is very little room for fraud here.

I don't know, if you're worried about that sort of thing I'd think there's a very long list of exploits that should concern you more than this quirky bounty program.

Just make the penalty for fraud very significant and award the truck drivers half if they can prove fraud happened (Dashcam video or something similar). Combined with city CCTV it should be pretty possible to work out who was lying in the case of a dispute.

Never, for like a dozen reasons