Years ago when I used to sell computer PCs and we were attending a tradeshow. A potential prospect came up and asked me “What is your warranty terms?” and I replied “We give you three years warranty.” The prospect was not happy, but instead of leaving the booth he stuck around there.
He then pointed to a nearby computer booth and said “They give a life time warranty, why don’t you give a life time warranty on your PCs?” I looked at the prospect and then asked “Whose Lifetime are you talking about, yours, mine or the computer’s?”. When you try to sell something the prospect has a right to ask everything they want.
it is your responsibility to sell your product for a cost and profit that makes sense to you being in business.