The only tool really is to look at the sales rank in the product details. It will tell you 'Sales Rank **** in dvds' for example - basically the higher it is, the faster it sells - with DVD's, for example, anything in the top 1,000 sells fast, anything in the top 100 flies of the shelves faster than you can blink, and if it's, say, ranked 15,000 you might sell one a week. However, it doesn't cost you anything to list, other than subscriptions fees, you just pay your percentage once the item actually sells.