i wouldnt think it was worth buying a used MAS. might fail on you. seeing that you dont know the history, i'd be skeptical.
it may have low miles, but how many of them were exposed to a over-oiled k&n filter?
also, i'm not sure if the C280 and the E320 and other cars he listed have the same MAS. I would think with the larger displacement engines, it would have a larger MAS and sensor to accomodate the flow.