Theres nothing to stop him saying "what accident" play this one carefully if you dont want to go down his route!
price up a bumper, allow 3hrs (£25 per hr) painting and fitting time, plus materials (£50), so you need off him around £125, plus the price of the bumper, plus vat..
If he settles for cash, you must still include the the vat, as youll still have to pay it, when you get it repaired
Also, I would never let anyone who repairs taxi bodywork, anywhere near my car!
Tom