cash or not, sell it at market price. maybe give few hundreds discounts at your own discretion, if the car's still within 1yr from the date of your loan, then finance company will charge you the interest for the whole year. if loan duration already exceeded 1yr, they calculate to the exact month you are selling it off (ie. 1yr 2mths). if below 1yr, you lose some interest (ie. paid 6mths installments already, finance straight away charge you 12mths interest)
let him view the car, if he complains here and there, then you estimate if you replace those things he complained will cost you how much. give him that discount, he'll be happy. then again, if your car is those not so hot selling type (ie. volvo, audi), got ppl interested, sell off quickly. i think after 15yrs old cars, you will have difficulties selling it as there'll be no loan available and ppl have to pay cash. with 25-20k cash in hand as down payment can get yourself a new car, 5yrs no maintenance headache.
my point of view
