compare what you are looking at to the listings for other comparable cars from other sources. For example if you see a 2020 model 3 LR for 50k but everywhere else they are 45k (similar features, miles etc) then its overpriced. (made up numbers). Its hard to find actual sold data and all the guides like NADA.KBB cant keep up with the market right now. All you can really do is compare it to what else is available in my opinion.