The one LFS I have left, some know and some dont. I know how to sex live bearers, and some other fish. The ma and pop shop that just went out, I think they knew, Im not really sure.
I went to my local chain store to get some paleatus cories and wanted a mix. I was a bit surprised that they couldn't sex them so I just told them one by one which cories I wanted from the tank. The local mom and pop types do know fairly well what they have in most fish but the hard to sex ones are as hard for them as for us. You can't fault them for not knowing when you know what to look for and still can't tell yourself.