I travel all over the world teaching advanced Java to professional programmers. Why should a company engage me? And how do they know that I won't take their money and not show up?
To take the fear out of the purchasing decision, I do two things:
They need to claim the guarantee within 4 hours of the course start. That is enough time to figure out if the course is for them or not. They cannot spend 4 days with me and then say: "Meh, didn't like that." If I cannot fix whatever they do not like, then they do not pay for the training. Plus, I pay my own travel expenses (that's where the extra 10% comes from).
A guarantee keeps us honest. You can imagine how hard I work when I present an in-house course. I give it my all. There is no energy left for social engagements or sightseeing in the evenings. The client and work gets my full attention. When I work, I work. Even emails have to wait until the course is over.
It is risky offering guarantees. A few years ago I was reading espresso machine reviews on Amazon. One reviewer had bought 8 different models for his team, unpacked them all, used them for a week, then sent back 7. He was proud of his genius in finding the best possible machine. According to the Amazon policy he could do that.
I also offer a 30-day money-back guarantee for my online self-study courses. The customers do not have to give a reason why. Within 30 days it is easy for me to process the refund. One click and we're done. I always have a look how much of my material they have looked at. In theory, someone could buy a course, watch the entire thing, then request a refund. This has happened. And I still give a full refund. As you can imagine, it does not make me feel particularly charitable towards them. It reminds me of the espresso machine guy.
Despite the risks for a business, money-back guarantees are essential. They reduce our customer's risk. The less scary a purchase, the better. It is better to refund too much than too little.
Kind regards from your friendly entrepreneur
Heinz