If you sell me a broken phone, it gets broken in the mail because you didn't package it correctly, or any other thing that can happen between the time you send it out and when I receive it, you should refund my money or accept my return.
I buy hundreds of thousands of products per month for my business on Ebay and Amazon and many people outright lie about the products they are trying to sell me. A good return policy is a must.
My theory is that it's one of the only reasons Amazon and Ebay became the kings of the online marketplace. I've tried to purchase from the other sites and because there are barely any protections in place for buyers, I always go back.