I understand your point, and I do not expect sales people to know everything about everything, but I draw the line at those who obviously don´t know what they are talking about but make an issue about arguing with you and telling you that you are wrong!
For example...
I went into a music store in Genoa (Italy) and asked if they had any flatwound strings.
He tried to sell me some guitar strings, to which I pointed out (my fault) that I was looking for bass strings.
Are you sure you want flats? What bass are these for? and I answered that they were for a Fretless Jazz.
"Ah, fretless, in that case you need flats" was his answer.
Well, obviously I wanted flats, but by now (after about 10 mins of converation to get this far) I was intrigued as to why I needed flats.
"Well, it's a fretless, all fretless have to have flats!"
"And why is that?" I asked, confused.
"Because it's a fretless, it has to have flats" he said in an irritated voice.
"But why??" I insisted.
"Because they are the only strings that work on a fretless!"
I assured him that my bass currently had rounds, and that it worked perfectly, to which he argued the point that I was obviously confused.
After another 5-10 minutes of discussion (geeting rather heated), he asked me if I played Jazz.
I said that I didn't, to which he suddenly brightened and said that he understood the problem, that my bass wasn't a jazz bass.
Unfortunately I have had lots of experiences similar to this!!