I think staff should have a rudimentary knowledge of what they sell. For instance if I go in to buy a particular printer /fridge/ laptop and I ask advice I expect there to be some level of knowledge or to be referred to that brands 'champion' in store.
For books I would expect them to at least say ' it will be in our children's section if we have any . Let me come with you to look'.
I'm sure Waterstones would be chuffed to bits to hear a member of staff just directed a customer straight to another store without checking /asking someone/ using the ISBN computer.
So to answer your question OP Yes I do think so. Its what can give a shop and edge over its competition.
"Old fashioned" expressions that young people have never heard.
I think most bookshop staff would look things up for a customer, so this member of staff was being either lazy or a bit thick.