My brother makes a pretty good living selling on eBay. He deals mostly with WWII memorabilia so he has pretty specific market. He spends his time at garage/estate sales picking up "stuff" and cleaning it up and selling it on eBay. He's come across some pretty rare finds.

One was an authentic Samurai Sword that was received as a ceremonial gift. He did some research on it and realized that it was worth more than he could insure it. He actually found the original family to whom it belonged and offered it back to them. They live here in the US now and it ended up in my brother's museum display for a while and I believe it is now on loan to a Japanese cultural display as the family did not want it back.

He's had some back luck on eBay, but also some pretty good sales. He has learned over the years what to do and what not to do.

I have sold some things on eBay, got burned once and learned my lesson on shipping. I buy on eBay but do my homework first to set my upper limit on pricing.

My husband buys a lot of rolling train stock on eBay as it ends up better price and better quality than what he can get in the local hobby store.