How does the rest of your post support your statement that's in bold? It sounds like the shop that you went to at first is both ignorant and greedy. The others you refer to fill the tanks. So what's an example of a shop that refuses to fill a LP72 that's NOT ignorant or unknowledgeable?
I was wondering the same thing but was afraid to ask?

N
). With the cost of traveling 50 miles for an alternative fill source this might be an economical choice.