Customers sometime chip their fixture after you have refinished it. They understandably call you to come out to fix it. It's not that you don't want to fix it, but you really can't charge as much as it might cost you to go out.
Be proactive and cut out these callbacks by giving your customer a small bottle of the topcoat you used along with some catalyst. Tell them to store it in the refrigerator and use it if they get a chip. Everyone is happy.