Make it a habit to open all your junk mail. I got a letter inviting me to review an item that I had recently purchased on Amazon. And if I did, they would send me a $30 Amazon gift card. I loved the item so I figured this was a good way to share my honest opinion and get $30 for doing so.
And they really did come through! I just added it to my account.
So let this be your reminder to open all your junk mail. You never know what you might find inside!