Flip job!
I think it depends on what the car is really worth. Say I paid $7k for a car just because the seller needed to sell that day or something, but it was really worth $12.5k. In that case, you're darn right I'd ask the $12.5k if that's what the market would really bear at that time. If I bought the car for $7k and it was really worth $7k, then I probably wouldn't get $12.5k for it if I tried. Unless I found someone who didn't know the market and has more dollars than sense.
Basically, if the car isn't worth $12.5k, it won't sell for that much. I'd just be crying for not being in the right place at the right time to get it cheaper. I think it has absolutely nothing whatsoever to do with what someone paid for something, only what it's actually worth.
I doubt it's worth $12.5k anyway. See what happens.