You will always get a few returns, I got one every 100 products or so - not that big a deal (unless its a high commission item!)
Don't forget the security it means to be paid by one of the largest sites/internet companies around. You know that you will get your check, you know that it will be good and if done correctly, your customer will be back tomorrow and perhaps buy some more. Quality always has and always will sell, generating long term commission and sales, shitty get-rich-quick and other nonsense will come and go, leaving you with nothing. Take your pick, which one do you want?
I have several amazon site, that I build using Associate-O-matic free. Still not any income... Can anyone give me advice?