Here is the dilemma. On an after-hours emergency, a customer says their water heater blew a temperature & pressure valve (T&P) and flooded the basement. The plumber evaluates the situation, replaces the T&P valve, runs the water heater through a cycle, cleans up, collects the charges from the customer, and leaves.
About a month later, you receive a notice from the customer's insurance company saying "Our investigation of this loss indicates that you are legally liable for damages to our insured's property."