I've seen and gotten several great deals here on BFC. In turn, I've sold knives at great prices, just to keep the good Karma flowing.
Often, with the way that the forum works, a knife can be marked down, and no one sees it for a couple hours, if it's 3-4 pages back. Always go down a few pages when browsing, and always check back on knives that caught your interest the first day, as discounts are inevitable, if it doesn't sell immediately.
Forums:
ZT 0550 with 2 custom scales: $105
ZT 0561 used $140
Protech Dark Angel $165
Lionsteel SR1-G Titanium $210
Other buys: Kershaw Offset 'used' $100 (it was essentially NIB)
Kershaw TiZDP Leek $125 used