I don’t know what your fear is. If you have a gas sniffer, then it’s real easy to determine if it’s either leaking or isn’t. Easy money, if they are willing to pay. You aren’t certifiying anything…just noting whether or not repairs have been performed. Let’s don’t get into hashing out that argument again, though.
Regarding the price, just say “I’m sorry you feel that way. Most feel my prices are reasonable. And this is a business, not a charity, and it’s how I keep my family out from under a bridge.”