Storage. Depending on how big your business gets, you’ll need ample room to store the books. You can’t get lazy or disorganized about it, either. You have to keep the books in good condition, and you need to be able to find them when someone wants them. For instance, if you list a book in “like new” condition, and then the pages get smashed during storage, you’ll be in a bind if someone places an order before you realize what happened.
Research individual companies in your desired niche: If possible, it’s always better to become an affiliate directly with a company (if they have an internal affiliate program), as no one else will be dipping into your commission rate. This is the preferred route for most of the prominent affiliate marketers, including Pat Flynn. Unfortunately, it’s also the most work, as you’ll have to do the research yourself to see who offers programs (they’re usually listed in the website footer).