My Dad tried several online sites when trying to sell an 11yr. old car. He found success in a place he wasn't really looking. Here are the sites that were referenced on the show.
Kelley Blue Book https://www.kbb.com/
Bid Lane https://www.bidlane.com/
Car Max https://www.carmax.com/sell-my-car
Carvana https://www.carvana.com/sell-my-car
Tred https://www.tred.com/
Consumer Reports https://www.consumerreports.org/cro/car-prices-used-car-inventory/index.htm
Edmunds https://www.edmunds.com/
E-Bay Motors. https://www.ebay.com/b/Cars-Trucks/6001/bn_1865117
CarGurus https://www.cargurus.com/
AutoTrader https://www.autotrader.com/