Yeah I took a hit two years ago when I sold my Session 8. However, I mostly have new clothing (see bits and pieces), so hopefully that retains it's value. I slashed them a lot already.I've used Facebook groups mostly lately, although mainly for what's left of my vintage stuff. I haven't really tried to sell newer stuff yet. I usually give it a month or so there, and then eBay.
However - be warned - if you need something to actually sell, be prepared to accept a sale price far less than original. Especially if it's 26". A $6K+ bike from a few years ago is worth maybe $2K now. Guys who bought some of the last 26" DH bikes really got screwed.