The top of the Targa bra has a bad angle (too viertical) and seems like it is receptive to catching stuff. Also, the front tire likes to throw small pebbles up along the forks, and onto the tank or into the riders lap, which can get caught by the bra. As previously stated, clean and polish regularly.
However, it is still the buyers responsibility to inspect everything before buying a used bike, so really your buddy can't. blame anyone else.