That's there discretion! to fill or not fill. But they should be trained in there service field or do not dispense the product. Flying J hires gas jockeys and they cover the propane fill too. There is a letter on ASME propane tanks if you search for it. there was also a article in FMCA a few years back. Get a copy and carry it and inform them politely.I believe it was in GS magazine too.
Propane Inspection:
http://tedjohnsonpropane.com/frequently-asked-questions-about-propane/#item_283
by Frank (Nanaimo B.C.)
Question: Do I need a propane inspection in order to sell my RV privately?
Answer: First, there is a differences between a DOT propane cylinder and an ASME horizontally mounted propane tank.
The DOT cylinder is removable and is subject to recertification 12 years after the manufactured date. DOT cylinders are portable and removable from the RV. When empty, you take them to a refilling station. DOT cylinders are found in travel trailers, 5th wheels, and backyard gas grills. With a DOT cylinder, you have the choice to recertify it (if you can find a recertification facility, which are not easy to find), or just replace it before the expiration date.
ASME tanks on the other hand, are permanently mounted horizontal tanks found in most motorhomes. To refill them you must take the motorhome to a propane filling station. The ASME tanks do not require recertification. They should still be inspected periodically for rust and dents. Eventually they may need to be replaced.
The general recommendation is that once a year you should have the entire propane system inspected for leaks, rust, and proper regulator pressure settings. The inspection should include all propane-powered appliances like a stove, refrigerator, furnace, hot water heater, and propane powered generator, etc. .
In selling your RV, we aren’t aware of any official requirement to have an inspection aside from what is stated above. In our view, both buyers and sellers should take steps to ensure that the propane system is in good condition and operating safely. In unsure, then call in a qualified professional to do an inspection, and definitely look at the expiration date on DOT tanks.