Personally I prefer shops that list what they want to sell. ie option A. If I am shopping online I will just go to the shop that shows stock, splitting orders between shops if necessary. If I am visiting a shop or phoning them up then I am likely to be doing it because I want advise, then I might be prepared to wait for special orders depending what the stuff is.
Shops that list everything but only actually have a small selection really annoy me
I would also say that, unless you have the time for aftersales support steer away from the stuff that is poor value or quality. It might lose you sales but they are probably not sales you want the hassle from?
That was certainly the approach I took when I did domestic electrical work. I refused to supply/fit bits that I thought poor quality as it was just too much hassle (for me AND the customer) dealing with the issues that follow. I can't say I saw any lack of work because of my attitude although it might be different in online sales where it is harder to "sell" the customer service side of things.