Perhaps. If customers are really doing their research and there is no other way to differentiate, sure. In a perfectly rational world for sure.
But there is a real cost of offering a money back guarantee: it may be distracting you from other issues. It may encourage a "throw stuff against the wall and see what sticks" type of mentality. Which can get you started, but random experimentation based on "best practices" and "do what the others are doing" is not the shortest path to very high conversion rates.
The real way to increase conversions is to "sleep with your customers". Get to know them so well, you know what their heart wants. You know the real reasons why they want your product or a similar one.
And then fulfill those desires. Give them what they want and explain it in a way that they understand.
But if you don't know your customer, which takes just a few days of conversation...well, you're throwing darts on at a "best practices" dartboard.
If you do your homework, you can narrow it down to:
I don't understand your product.
I understand your product, but I don't see how it would help me.
I don't trust you.
I can't figure out how to do X on your website.
Your product is priced too high/too low.
A money back guarantee does nothing to address to above 5 objections.
A guarantee is only useful if:
1. You need to lower perceived risk of using your product. 2. You need to demonstrate confidence in your product.
There are dozens of other conversion problems that won't be addressed by a money back guarantee.