I was pretty active on Head-Fi at the time and snatched up this deal when someone posted it. I think the HD800 was still $1500 at the time.
Though that is probably not even my greatest "steal", which could be loosely seen at actually stealing. I bought the Fostex TH-900 from a relatively new online vendor, and they accidentally sent me 2 of them. I checked and legally in the US when a merchant sends you something you didn't order, you aren't required to send it back. I held onto it for a bit and that company never contacted me about it and I sold it new in box for $900. I guess they were too disorganized to notice.
I'm not all entirely lucky or wise with money. I bought the Hifiman Edition X on release for $1400 and similar tier headphones like Edition XS are less than $500 now. But I still like them enough for it to be a permanent part of my collection.
