I am also curious as to how they are able to get around Amazon's affiliate agreement.
"You will not offer any person or entity any consideration or incentive (including any money, rebate, discount, points, donation to charity or other organization, or other benefit) for using Special Links (e.g., by implementing any “rewards” or loyalty program that incentivizes persons or entities to visit the Amazon Site via your Special Links)."
They may not be worried about getting around Amazon's TOS.
Purely hypothetical but a potential strategy could be to ignore Amazon's TOS in the early stage and use their breadth of products to entice new users and build critical mass. Soon they get to be big enough that Amazon take's notice and cuts them off. However by that time they have enough momentum and users that they can keep their users happy by offering all the products available through CJ, LinkShare, Share-a-Sale, and their own in house sourced affiliate partners.
"You will not offer any person or entity any consideration or incentive (including any money, rebate, discount, points, donation to charity or other organization, or other benefit) for using Special Links (e.g., by implementing any “rewards” or loyalty program that incentivizes persons or entities to visit the Amazon Site via your Special Links)."
Refer.ly clearly violates this.