It always depends on the car, whether you are buying private party or from a dealer, etc.
Some cars hold their value very well. Prius is one of them.
But a friend’s son had to sell his 2 year old prius – and took a big loss… so deals occasionally happen.
I’ve also found that dealers ask well over KBB for used cars, and offer well below KBB on trade ins. So dealing with a used car (either end) with a dealer is a bad proposition.
I’ve bought and sold cars privately – in general I’ve gotten (and sold) for below KBB because that’s the market price.
So if you want a deal on a used car – start scouring craigslist and the reader.