I do the same for cut vinyl on vehicles. One customer scratched the letter E on his rear van door 3 times with his toolbox over several years! Very good customer, I replaced all 3 times and we still laugh about his clumsiness years later. His business over the years more than made up for the few minutes I spent replacingWe don't explicitly state a warranty. But in general, we'll fix/replace stuff if they fail within a year (or so, depending on what it is.) We do tons of cut-vinyl car lettering. If someone comes in with scratched panel or other failure that was their fault, as long as they paid full price (I have a few groups of customers who get a ton of stuff from us for a sizable discount, those people don't get this benefit,) I'll usually fix it at no cost. Magnets, no way. I'll often help people out with banner failure, but I also regularly get between $6-$8 sqft for them. I'm not losing a customer over something that cost me $15 and 15 minutes of my time.