“Too many saves” is annoying but my garage is mostly clean now. I don’t see why you can’t just paint every car, though.
I use my favorites for cars I race with, so this wouldn’t work for me necessarily, however I get the idea of flagging the cars some how. If you don’t own all the cars, and don’t favorite the cars you use, then yeah, this works quite well to mark cars you want to sell… one of the biggest PITA for me is digging through the garage to find the dupes in the first place. This is why I reply instead on the “new” flag for selling/gifting in my own garage… Same concept, different executions.