I'd give him the whole right fist if I were you.
Back in my younger, more naive days, and boy was I naive, a bloke knocked on my front door and inquired as to whether the Citroen AX, that had been my car and was sitting on the drive for ages, was for sale. I said that actually I didn't want it anymore and it was taking up half the driveway, so I let him have it. He claimed he "did AX's up". I should've worried when tax and MOTless and with the handbrake sticking, he backed it off the drive and drove off with it.
Two days later I got a phone call from Surrey police, saying that the shell of my car (as the paperwork hadn't gone through yet) had been dumped on the side of the road in Guildford or some place and had the engine missing, and that as it was my car I was in charge of moving it or being fined! Thankfully after explaining the predicament to the officer, he agreed that as I didn't live nearby he'd scrap the car for me.
A lot of hassle for me being stupid really. My mum was sad though, because that had been the family car before it was solely mine...