Buyers usually take the risk upon themselves by giving you money in exchange for questionable value. The value is only revealed when the buyer starts using the product.

You can minimize that risk by offering a money back guarantee, easy return policies (no questions asked money back guarantee, free return shipping).

The point of guarantees is not to make getting money back easy. Yes, it should be easy, but if your product is good, you will have very little amount of people actually using it.

The main point is that is reduces risk and relieves worries people have, and thus helps to minimize friction.