This episode only proved Stan was right the first time around.

They did pay for and get the windshield fixed. Benson should have never hired the bounty hunter in the first place.

They returned the car to him already. He should have never hired a "shoot first ask questions last" hitman and pin it on them. He became at fault for that.

I disagree. Mordecai and Rigby actually got the windshield fixed. Benson should have called it even instead of pinning it on them. Who in their right mind calls a HITMAN? Benson became more at fault for the destroyed car in the end.