The first thing to think about when selling anything online threw a store, is are you the cheapest price for the product your selling? Because if your not then I can assure that you will lose most of your customers to the store that has the cheaper price. People will more than likely copy paste or type in your product to Google or Yahoo and find ten other places that sell the same item and see what they are charging and if they are cheaper more than likely they will buy from them and all you did was help your competition find a customer.
So when i choose and affiliate program i took a look out there at every one and choose the one that had the cheapest price on products available and then choose the cheapest commission possible thus making the prices even lower in the store. In these two store i wanted to sell just adult movies and videos and make sure that they were the cheapest anywhere on the internet that i could find!