Folks do put on airs.
The machine/fabric snobs--it is their shop and inventory, they may only work on specific brands, but there is a polite way to treat people, even if they are not customers today. I, too, have experienced curt answers when inquiring about machine repair. A polite explanation of franchise rules would only take seconds more than the brush-off.
Our late, lamented local Singer store sold Singers but the repairman would work on anything. The sales staff were always patient and polite.