How about condition, mileage, abnormal wear, smoke smell, mods, stock?, upkeep, scheduled maintence, area, color, noises, etc..
There are waaaaaaaaaaaaay too many variables for that general of a question. OrangeMSP got more for his trade-in than he bought the car for but he also had MANY mods done to it. I would get considerably less than 10k for my car since I have >30,000 miles on it and smoke in it along with a book of warranty receipts.