When it come to eBay there are pretty much two ways you can approach it.
1. Hot selling items, of course the market is always firing because there is plenty of buyers for the products.
The negative aspects of these products is the competitiveness between sellers that forces very low margins. It's an increasingly difficult market to drop effectively into as more and more suppliers are moving to wholesale business models to ensure the cheapest possible supply prices.
2. Niche products. A niche product is one that there is buyers for, but is being under supplied.
Of course the fact that the market is under supplied means that sales of these types of products can still be very strong. However the negative aspect of targeting a niche market is the research side.
No top 10 list of hottest selling products is going to have niche items on it, so you are starting with pretty much a blank page. You have to somehow identify a niche market, then identify a supplier to cater to that market.
If you're cashed up, can afford to buy in bulk and rely on volume sales to make your money, then getting into the hottest selling items would be the way to go in my opinion.
That said, if you don't have those sorts of resources open to you, then I would be suggesting either settling in for doing some serious researching into a niche market, or just jumping in somewhere in the middle.
Every day products, second hand items, consumables, that type of thing. They won't be the hottest selling items, nor perhaps turn out to be niche products, but they still sell everyday to everyday kind of buyers.