I generally tell customers that if we have any in stock it would be on the floor, if not we've sold out as we generally keep shelves full 99% of the time. I've been there for a few months now and still not been taught every process (including the warehouse out the back and how/where to replace items if needed). Something that doesn't help is when customers don't give information like product name or EXACTLY what they are after but just offer a generic description, I had to help someone find a kitchen place mat set the other day.... but they didn't call it that. And yet I was expected to know what they were talking about.
Depending on who you ask, some upper management expect us to deal with every customer request - other upper management tell us to fob the customer off and send them to the proper customer service employees instead.
I have mentioned it before but whenever customers ask where item x is, I'll personally escort them to where it's located. Whereas most people will just say "over there a few rows down to the right". I usually just say "follow me" and walk them to the area in part because I am useless at giving directions, I might say 4 aisles to the right... when it's 5 or 6. There's that and the store changes the layout every 2-3 weeks so a lot of items are in different spots to where I last remember seeing them.
The second point irritates me as a customer, heck even as a worker I don't really talk to anyone I work with unless I have to while working on the job (either asking them where something is or where someone else is that has what I am after etc). I also feel awkward and somewhat guilty when doing so eg: Prior to starting my shift i'll have a general chat with the person checking the bags of customers as they leave the store, yet I'll always stop the conversation when there is a swarm of people walking out.
