Very, very rarely, and when that happens I just file an inquiry (you can do this once your order is 30 days old) and they have always credited me at that point with no problem. I have made numerous large purchases and have never really had an issue. I am almost at $1,500 total in cash back since I started using Mr. Rebates a few years ago. They are my main cash back website I use because of their reliability, but I do also use ShopatHome and Ebates on occasion if the cash back percentage is higher than Mr. Rebates. So I would say to shop away with no worries! Enjoy the free money!