Erm, I have no idea who or where this trader is or if the damage that is apparent on your car is caused by "shoddy" workmanship or carelessness, but that is no way to return a car to anyone, regardless of whether it's a replica wing or not.
If the "tradesman" who did this job was honest and upfront re the possible outcome to replace the wing, then fair enough, you take your chances, if not then it's a very dissapointing lack of respect, to you firstly. and then to himself for trying to pass this job on as acceptable.
It's not acceptable to leave someone's car in this state, then try and charge a further £100 to rectify, that is just downright pis5 taking. As has been muted, if the "Trader" is reputable, then I'm sure he will put it right, if at fault. If not at fault his side of the story would be useful.
Either way, there are aspects of this that would make me steer clear of this particular "Trader". I would not accept a job like this, nor sir, would I have paid upfront for a job, a deposit maybe, although I've never had to do this before on a small job, of this size.
I sincerely hope that both parties come to an amicable solution