It has been shown by many of the most successful online retailers such as Asos, Kogan and many other online stores - that the longer the money-back guarantee is - the greater positive impact on conversion rate.

The principle is simple: consumers are scared and nothing instills confidence more in them than saying to them: "We'll happily give you your money back if you're not happy."

For many profitable E-Commerce stores, they've found the increase in profit and conversion rate as a result of implementing this strategy to far outweigh the cost of the refund rate.

You could also consider offering a guarantee that's based on results, but that works only if the customers can relatively easily measure the impact the course had.

There is also a way to offer a money back guarantee, if it meets certain conditions.