My opinion,
eBay is fine, I've never felt poorly treated.
Buy a David Clark. They are more expensive, but worth the extra. I'm not saying that there aren't other good ones too, but David Clark offers consistantly good quality, and even if it's 20 years old, it will probably work like new. I've rebuilt and used DC headsets which had been submerged for days. They dried out and cleaned up well, and worked fine. Things like the quality of the wires and plugs may not seem important when you're buying, but they will when they stop working a few thousand feet up one night!
I'm still using the DC headset I bought new in 1980. I've replaced a few ear seals, but other than that, it's still working perfectly - the quality and reliability was worth the extra money, and so is my hearing! You gotta like the Bose NC, but I'm not in the group that can affort those. I owned a DC ANC headset, but was not pleased, and sold it. Make sure you get a newer mic, not the older carbon. Otherwise there might be slight incompatability with intercom users.
Cheers, Pilot DAR