the wallet is usually found by the next passenger, now that dodgy person can either hand it over to the dodgy driver and hope he/she hands it off the police station (not usually) or the passenger decides to hand it the police station or takes the money and dumps the wallet into the nearest rubbish bin.
A friend left her latest iphone pro max in a taxi last week, she only realized it after a while and then frantically started calling her own phone, luckily it was picked up by the next passenger who told her where they were and she went to pick it up. It could have been a costly 10K mistake lol