Wilson then switched to a new method of buying money: Amazon Payments.

The No. 1 e-commerce retailer is now trying to challenge PayPal in the online payments world, and to gain traction, it's offering person-to-person payments without the fees charged by similar services. So, you can load money into your Amazon Payments account using your credit card, allowing you to rack up rewards for free. And while Amazon says it will shut you down if it finds that you're sending the money back to your own accounts, you can always "pay" a spouse, family member or trusted friend who has agreed to give you back your cash.