If you have never had success with Amazon, you need to consider how you are using the ads, and on what type of hubs you are using them on.
Simply putting an Amazon capsule on a hub that is not particularly commercially orientated will never pick up more than the occasional shopper. With an affiliate that offered a 30 day cookie, you can count on a few going back to purchase during that time, say, at the end of the month when they get paid. With Amazon they need to be convinced by your hub, or better still, in the buying frame of mind when they arrive at your page.
Anyone searching for a particular product is likely to be looking to buy it.
With Ebay capsules it is a little different, as visitors may be enticed by a really low price.
My advice would be only to use Amazon on a product related hub, to use it sparingly, and to select specific products which you are writing about.
Also, to make money on Amazon you need traffic. If you hubs are getting a couple of visitors a day, you are not going to be generating enough clicks to get sales.
Have a look at my hubs on Amazon for a few tips.