There is no single answer to this question. The answer depends on who you are. Looking for eBay items based on profits is a recipe for failure.

Instead look for products where you can compete with other sellers on something other than price. I regularly get more money for the trains and toys I sell on eBay because I specialize in them.

Last week, I sold some train sets from the 1950s. Based on past eBay sales, I expected to get $60-75 per set. I got $120-150 per set. The extra profit is because I knew exactly how to describe the trains so a collector would feel comfortable buying from me. In other words I removed the risk of buying.