Hey Chisme,
Why not just take the panels off the moped and when he asks for the money, say you cant afford them and give the panels back? and also say that you dont want to see him again, because he's been acting like a fucking loser. fuck the money, if you should beat him for anything, it'd be for the way he's treated you. if he nicked the bike then he can nick something else for £50. In fact you should definately fuck him up, bike theives are fucking scum, how would you feel if someone stole your ped?