Counterfeit BMW parts. Take for example the Mass Air Flow sensor I bought on Ebay. It totally screwed up my engine. Why? There was a cheap faker circuit that would fail every cold winter day making the sensor alert system give false indication for air intake sensors which would have resulted in costly repairs. The real MAS have an expensive platinum wire that senses when the wire becomes contaminated. My fix was to remove the counterfeit MAS and create a better cleaning method for my old MAS.