I wouldn't pay $12k for a car that's been modded to the moon as a matter of principle. Mods don't add value to a car, they detract from it, and I'd steer clear of a 10 year old, turbocharged Subaru that's been heavily modified.
I can't emphasize enough the dumb stuff people do to these cars. Even if the car was intelligently modified, the chances are probably pretty high that he was beating on it every chance he got. Who increases the performance of their car and then doesn't make use of it?