Opinions on Money back Guarantees?

Hello and good day!

I have read in many books that it is a good idea to offer a money back guarantee on products you sell.
I offer all of my digital downloads to members after they sign up.

My questions are:

– Should I offer a money back guarantee at the risk of the possibility of some people signing up and canceling just to get free products, but at the same time increase trust and value to my customers?

– Or should I continue not offering a money back guarantee but risk possibly less sales?

– What can I do to protect myself?

– What are some of your opinions and experiences?

Thank you very much for your timeand have a wonderful day!