[asr]

The problem is, even if you add more filters, used cars are still different enough from each other that your users likely want to see the hidden results--unlike airplane seats, where some results are more expensive tickets with an additional connection and therefore 99.9% of searchers will agree that result is worse.

What if there are two cars, one of which is $250 more, but which has a few (fairly minor) additional features and is 75 miles closer to the user? Figuring out which car the user wants to see is a hard problem.

That obviously doesn't mean it's not worth working on, but my guess is your current solution is sub-optimal enough you'd be better off displaying all of the results and simply ordering them based on these criteria. Or at least making it very obvious to the user there are other relevant results, since most people are used to all relevant results being displayed in one long list (that's my guess; I'm not an expert in this at all).