Guarantees make people feel more comfortable with buying.

The longer the guarantee, the more sales you're going to make. It's a basic direct response rule.

There aren't as many serial refunders as ya think. That's simply a part of business and a part of life. I don't care if you're giving away a $30,000 product for $10. There will always be a certain amount of people who refund it - however, it's probably not as high as you think.