I've not seen the 110% money back guarantee in the wild however but it feels like a memorable offer. You'll have to carefully figure out how to avoid getting taken advantage of but I feel it might be a worthwhile risk.
I vaguely remember some book author having an interesting typo related policy. His claim was, for each typo reported in his book, he would start out by paying 1 penny, and for the 2nd typo he would pay 2 pennies then 4 pennies then 8 pennies and so on. It was a crazy claim because if you double your pennies 30 times, it's over $5 million dollars. I can't remember who did this, but how's that for an incentive to buy the book haha.
Kind of scary how inaccurate my memory was on the exact strategy, but that's definitely the one I was thinking of.
I recall it being a sports nutrition business but selling something reasonably unique. I would estimate that it would be an average sale of $50-$100, perhaps a high of $300?
So long as you're making decent sales an occasional hit of $5-$10 and the even rarer hit of $30 is hardly terrible.
After reading the comments here, I could be wrong.