I'm not really a shop assistant or clerk or cashier or anything..i don't really have a title, we're really informal (I guess at other stores they're called general managers), but in my position I do have a fairly in depth and intimate knowledge of our inventory. I know what we do have and what we don't; sometimes down to the unit.
However, there are times when I don't know or that I simply lie.
-If I am assisting a customer (or anyone else including my employees and/or suppliers/vendors) and you rudely interrupt, then I am going to be less inclined to actually check for you. I have had customers physically place themselves between me and the person I am talking to and tell me that I need to check "in the back" for an item they are looking for. That's certainly not a way to convince me to help you.
-All of the POS computer systems that our cashiers use have direct access to our inventory system. The cashiers generally know if its in stock or not. So if I see that a cashier or other employee has told the customer that we are out of stock, and then they approach me asking me to check in the back, I'm probably not going to do it.
- If the customer is acting in a manner that is just generally disrespectful, then I'm definitely not going to put any effort into helping them.
Also you have to remember, that in many cases, you may not have been the first person to ask for an item. In that situation its unnecessary to 'check the back' for an item; because we have already.
On the other hand, when I'm dealing with any of my regular customers or any customer who approaches me in a respectful manner, even when I'm certain that we are out of a particular item I may walk to the back and do a double check or even bring up the inventory system on the laptop and let them see that we are out, just as a way to show them that they are valued and that they're worth a bit of extra effort.