Sorry to dig this back up, I suspect I've picked up a fake pair of Momentums as well, but was wanting some help with figuring that out.
I bought a pair of 'near new' over-ear momentums from New Zealand's version of ebay - trademe. Everything physically about these headphones appears legit, the cables are the right colour, I have the bender on the end, everything is properly made, quality parts that feel correct.
But they sound pretty much awful. Bass is essentially non-existent and the rest of the frequencies are barely better than my 202s and the sound-staging is fairly narrow.
The previous owner says he put about 14 hours on them and there is some signs of use - cat hair caught in the case, that kind of thing.
I'm planning on seeing if I can find a demo pair of these in a local store this weekend; any further thoughts on how I might be able to further deduce if these are legit or not?