I bought and sold a pair of HD580. Don't remember why I sold them. Then a few months later, someone was selling 2 pairs of HD580 for together for $200. I think one of them might have actually been the same ones I'd sold. When I bought them the seller said they'd been refurbished by Senn, I mentioned that when selling, and then one of the 2 pairs I bought was described as refurbed. It came with almost unworn pads, and silver drivers.
I bought the two 580's for $200 and promptly sold one pair (the older of the two pairs, with worn earpads) for $150. Great deal. Later on, I ordered a new pair of HD650 drivers and grilles and sold the 580/600 drivers. Didn't cost me much.
Bought and sold 2 pairs of HD555, 1 of HD595 and 1 HD598. I go back to these because I like the comfort and the 1-sided cable is much more wieldy than a 2-sided cable, but the sound quality is disappointing once you've been spoiled by the 580/600/650.
I've bought and sold several pairs of Energy Connoisseur C-2 bookshelf speakers. They're great, but I already have a matching system of the later C-3, etc speakers. The C-2's look better, so I always want a pair if I see them going cheap, but I sell them because I don't really need them, and they're getting long in the tooth and the drivers aren't easily replaceable. Also I've bought and sold at least 4 Bose Sounddocks that have been cheap on Craigslist. It's the one Bose product I like, it has some nice qualities, but I have enough speakers to put a real stereo wherever I want so I always sell the Bose for a profit. (BTW, there are Bluetooth adapters for $10 for the Sounddock. It's a good way to get a cheap Bluetooth speaker for home use.)
