It remains to be seen which ones will succeed. I love eBay. I have never been to a public auction, but I spend a lot of time on eBay. You can both save and make money there. If you can make something that people want and that is easy to mail, you can turn a profit.
Research is easy.
All you have to do is browse around and see what people are selling successfully. However, there are incredible deals to be found. Try searching for things like children's clothing, toys, jewelry, collectibles, books or whatever you need. The secret to winning auctions is to come in at the end and make your bid. See how much time is left, and then put in your bid 5 minutes beforehand.