In Amazons defence, they offer you a near unlimited choice of products to advertise, if you have targeted traffic I think it would be well woth incesting some time in to doing some A/B testing on the products you are advertising, and how you are advertising them. The fact that you are making low sales if you have traffic will be more down to what you are doing than Amazon.
The amount of money you can make can depend greatly of you budget. If you have a small budget and you don´t have a lot of money, then you have to start with free marketing methods like article writing, blogging, forum marketing and such. It takes a lot more effort ant time to have success with these methods. But they are very effective if you keep writing articles and participate in forums. You can make $100 a day within just a few months just with article marketing.