Very good point, this happened to me a few months back.
I was in a room with some great shuffle heads, top class clean guys who I'd raced before several times. One of them made a mistake & went into Degner very slowly, this enabled me to get along side him before the exit, the second corner. Anyway, I left him a cars width on the exit as I'm a polite racer, however, he ended up in the sand. I felt absolutely no contact whatsoever through my wheel, so concluded that he binned it himself.
Then, he starts bad mouthing me & swearing at me for the rest of the race which puts me off & I make a mistake & end up hitting someone else off. After the race I appologise to the guy I accidentally hit off, but not to the first guy cos I felt no contact. In the next two races he decides to take extreme vengence by ramming me into the wall at every opportunity.
I decide to leave the room & veiw the replay that I saved to see what actually happened. It turns out that I did leave him enough room & that our cars never even touched, we were about 1 or 2 feet apart. I veiwed the footage many times & from several different camera angles & guess what? When I watched his onboard footage, his car appeared to be hit & pushed off track, whereas my car was nowhere near even touching his. Conclusion? I put it down to GT5's lag plus poor colision detection, I presume that my car lagged & hit his car on his screen, while on my screen I was keeping an acceptable distance.
And, the moral of the story is; DON'T ASSUME FELLOW CLEAN DRIVERS ARE DIRTY & RETALIATE AGAINST THEM! CHECK BOTH REPLAYS FIRST!
Because of all the verbal & on track abuse, this guy is now on my blocked list. Shame on him!