A handful of years ago, we were in line at a Flying J waiting to get propane for our Class C. The folks in front of us had an older Class A. The employee came out to fill his tank and told him the valve was too rusty. The RV owner challenged that he knew the tank was rusty, but he didn't have a problem in the past filling the tank. The employee called the manager and they filled it without issue.
I honestly think in situations like yours, some people are either afraid to try, don't know how to use an adapter or just aren't thinking straight. The Flying J by our house that we use to fill Propane tanks and cylinders has an assortment of adapters to fill different Propane tanks and cylinders.
-Michael
