I have been buying custom and production folders since the early 1990's. I have never returned a folder for a warranty issue. I have owned hundreds and used hundreds of knives. I think most returns are operator error or using the tool for the wrong purpose. Unless there is a manufacturing defect, no returns. If you screw up your knife by taking it apart you should have to pay for repairs.
Personally, I find the lengths manufacturers have gone to coddle the customer is ludicrous. If the knife is broken when you buy it, yes it needs to be fixed. If you used it for years and it failed, no warranty. I have some folders I used so much they just wore out. Over sharpening, lock travel issues and loose pivots. I retired them. I was thankful for the service they provided me. No tool lasts forever when it is used.
This line of thinking applies more to folders than fixed blades.