You determine what it is…
You determine what it is worth by getting a few offers- dealers and the two big car buying companies, and then checking for sale ads. The dealer offer is wishful thinking by the dealer on the low end, some of the for sales will be wishful thinking on the high end. The difference is your range. Then decide where in that range you wish to sell. The low end of the range is hassle free to sell at and the high end may involve time and hassle. Decide on the money vs. hassle ratio that works for you.