Refer.ly itself won't be able to be "gamed", they will only pay out a commission for a made sale, so there is no risk to them. Are you talking about someone "gaming" other user's links and replacing the original placer's tracking id with the gamer's?
The Amazon problem could be harder to manage as they scale since they can't do subid tracking per user and probably try and correlate redirects to specific Amazon purchases, but that is going to leave a lot of grey area for any other purchases the user should be credited for but turns out to be too difficult to correlate.
The Amazon problem could be harder to manage as they scale since they can't do subid tracking per user and probably try and correlate redirects to specific Amazon purchases, but that is going to leave a lot of grey area for any other purchases the user should be credited for but turns out to be too difficult to correlate.