I had a mk3 cortina ,, in blue and it looked a million dollars ,, a friend borrowed it and rubbed the back door against a bollard in a car park , no big deal , quick fix , off I went to sand it and fill , the back door skin was made from brown parcel tape , the sort you had to wet and let dry ,,, but it was done so well that you would never have guessed ,,, some folk are very good at hiding things.I have a friend who’s a wizard when it comes to filler (and fibreglass). He’s a decent welder too, but I still say I’d never buy a car off him!