There's a good guide at Beginners' Guide to Potentiometers that includes the following table:
Being from an electronics supplier rather than from an old piece of equipment I'd say the A is logarithmic and the B is linear, but it may also vary by region. You'd hope the staff would be able to confirm but it sounds like that's not the case? You could also consider buying online from a place like Digi-Key or Element 14 where they will be properly documented.
This is a bit of a guess but I'd say the W stands for wirewound, they normally have a higher power rating than regular pots and one likely sign is that they'll tend to be slightly larger and more expensive than the others. If that's the case they are normally linear and doing a search at Element 14 all 202 results for a wirewound pot were linear.
But based on e-bay search results it looks like the W suffix is commonly used for pots intended for balance control that have a center detent. Here was the resistance curve shown next to one product: