I used to have really good luck selling several used cars in the Auto Trader publications and cragslist.
It seems that in the last six years or so, as the con artists and scammers have really come out of the woodwork and infested the internet, that it has become harder to sell that way because you have to sift through so many bogus, cretinish cons to get the few people who want a car.
Economics seems to play a part, there have been times when low mileage used cars and new cars have been competitive in price.
My last car, a 1995 Infiniti Q45, was very difficult to sell online compared to my many successful earlier sales. I had to keep posting it periodically every couple of months, it accumulated an additional 30,000 miles, then finally one person came over and paid cash for it for cheap just before I was considering donating it, but it did have over 125K miles at that time.