I received an actual, authentic Mann filter in the mail today. Either today or tomorrow I'll take side-by-side pictures of the two filters showing how to spot the differences. Even the supporting "instructional" document is identical, but the printing quality on the fake one is very poor.
My guess is that the people selling these on EBAY are 100% aware of the fact they are fake. I'm sure these filters "work". I mean, how hard is it to make a filter? I just think you're not receiving the same quality of filtration.