The first time one gets into the car one can generally say whether one likes the car or not. Trust your nose. Certain unpleasant smalls just can't be got rid of. The first (used) house we bought had a not very pleasant smell in the entrance hall. Even though we renovated completely three times, the smell was still noticeable, at least for us it was. Think about it, most of the time you spend with your car, is inside the car.
We've already mentioned the fact that disagreeable things can be hidden under coverings. This is valid for foot-mats and particularly for carpeting. Try to get a look at the floor panels, at least on the sides. Damp is of course, absolutely unwanted. It could indicate that the windscreen-sealing is no longer intact. Indeed, water can get into the car from other places. Through faulty seals in the front bulkhead or because of defective drainage in places where water can gather.
Should the owner of the car be present, don't let yourself be appeased. Always assume the worst damage, the respective costs and the discomfort. Workshop prices are high and you can't really be sure whether the repair was successful or not. Rather take someone along, who has a tendency towards scepticism. 07/13