A lot of good answers already, but to add a slightly different perspective: I'll always add a money back guarantee to any SaaS product where it makes sense. I

A lot of good answers already, but to add a slightly different perspective: I'll always add a money back guarantee to any SaaS product where it makes sense. I believe it helps conversions, but I don't have data to back that up. What it really does is help more easily identify the type of customer who would be a pain in the ass and costly to support, and give an easy way to fire them without it being a straight up "we don't want your business". Instead, its a "we're sorry we didn't live up to your expectations, per our guarantee, we're refunding you your last month and deactivating your account." or something to that effect, with variations based on circumstance. It turns a likely negative customer support interaction into a potentially positive one.