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)."
"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.