Earlier yesterday (Friday), there was a series of used M9 postings on Amazon, at ridiculously low prices (500 - 1500 USD). They appear to be from newly created sellers from around the US. Their scam is to send you an invoice outside of Amazon in the hopes of you paying them directly.
I did some research on them and they are not limited to M9s, so be extremely cautious.
While I haven't seen them on eBay, we should be on the look out for them there as well.