Successful affiliates can make serious money but these guys generally are well established and are good at marketing using email.
All things considered, I am favouring the idea of selling on Amazon utilising either Amazon's FBA or a dropship model. I have been wanting to learn as much as much as I can about selling on Amazon and there are some decent sites teaching the basics.
From my experience, however, of reading content about successful selling on Amazon is that they provide good info until when it comes to the vital part, which is the sourcing of products. Invariably, they will point you in the direction of importing from China. But do you know how much headache that causes? Products are either generally second rate or the cost of import too excessive, leaving margin wafer thin. More work than it's worth.