Alan,it is called 'Spoodling' in the car trade,the idea is to see if you can make a car that looks as if it has never been on the road,the main areas that require spoodling are as follows-
1/Paint the tyres black.
2/Renew the rubber brake pedal,clutch and accelerator pedal rubber boots.
3/Around the door key areas they look scratched and awful,try rubbing compound first for mild scratches,spray bad areas.
4/Remove all traces of fluffy dices,steering wheel gloves etc,ie make it look as if it was never owned by anyone !
5/Steam clean the engine and spray with WD40.
6/Renew the number plates with new ones,they stand out like a sore thumb.
If the car is on the forecourt more than 3 days then you have done something wrong and need to sell it onto the trade.