Do you give a money back guarantee?

I've heard a lot of people saying how they've been ripped off from sellers on Fiverr so much so that they've decided to stay away! Their belief is that because they are only charging small amounts of money, they don't put much effort in, don't care and are here just to get as much money as they can for as little work as possible.

As far as i'm concerned, business is business no matter how little you charge. If it wasn't for the people putting their trust in the sellers and buying their stuff, they wouldn't have that extra income, so why wouldn't the sellers want to treat them like gold?

Obviously, there is a limit as to how much work one does for $5 but still, the work that is done and the service that is provided for that price should be quality.

That brings me to my decision, after a bit of a rant [ ;) ] to offer a money back guarantee on my new service - ebook cover design. As far as i'm concerned, if you're not happy, why pay? Yeah ok, there may be some people who will take advantage just to get something for free but I believe most people are genuine and honest and won't do that or is that my naivety [ :-/ ]

Anyway, do you offer money back guarantees and what has been your experience in doing so?