I was looking at a car in the showroom when the salesmen told me the car had a four cylinder engine. I had to ask why it had six plugs-))
I think the best at camera shops is when you ask for something and they tell you they've never sold it and you point over thier shoulder at the box on the shelf. The local place keeps all the sheet film,bulk 35mm and 120 in the fridge. If I actually buy film from them 50% of the time I just point and mention the colour of the box.