Gail, your local codes and regulations may have some say, so be sure to check the laws in your area. There’s a couple ways to look at this; is it a private sale between private parties? Is it a retail sale from an RV dealer? Is the RV advertised or noted to be “as is?” Is it a used or brand new RV?
Typically the seller will/should reveal any discrepancies within a private sale, but there’s no law or requirement that I know of, that mandates honesty. I always recommend an aftermarket PDI (pre delivery inspection) be performed to acknowledge any and all faults with that RV at that given time. The cost should be shared by both buyer and seller since the seller is able to verify he/she has a pristine RV for sale, and the buyer will be informed of any deficiencies that exist and need attention. Check out these recent questions to the RV Doctor Column for my reasoning:
Pre-sale RV Inspections
As a private seller, I would most certainly have a propane leak test performed before selling any used RV so to avoid the liability in case something drastic happens. But that’s just me. Bottom line, you’re only talking a minimum charge to “test” the system for leaks. And if a seller really wants to sell, he’ll pay for that service. Likewise, if a buyer really wants that RV, he’ll pay for the leak test. But I’d still suggest a PDI be performed by a professional service technician since any issues can be considered bargaining chips for negotiating the final price.
As an aside, in order to properly perform a propane leak test following the recommended RVIA procedures, as well as a couple other regulator tests, it requires an accurate manometer as well as a propane test device as pictured above.