This is called cookie stuffing and it's not only against TOS but also fraudulent and very illegal. You're stealing money from Amazon. The owners of Digitalpoint just got charged with wire fraud for this practice. If ethics don't concern you, you should stop simply because of the low relative reward and high risk.
It would surprise me if Amazon doesn't have an effective automated way of detecting this. It would be easy to detect based on user behaviour when they hit the Amazon page, and Amazon isn't known for throwing money away like that.
