Howdy all,
Thankfully most customers are actually very honest and the few dollars that you would save by NOT having a refund guarantee, would be quickly lost by the sales you would lose by not having a guarantee.
I have tested guarantees in many niches and always found a significantly better sales conversion rate with a refund guarantee of at least 60 days.
You can help keep your refund rate low (and thus improve your "stick" rate) by such things as;
Over deliver and exceed your customer's expectations.
for eg. Offer a surprise additional bonus soon after purchase.
Make sure your product does what your sales page says it will.
Promptly manage customer support issues.
Stagger your content (depending on your product of course).
Having a clear and prominent refund guarantee removes that lingering question is many people's mind "what if I don't like the product".
We want to remove as many buyers objections as possible.
Anthony