Yeah, you have to consider the perspective from both sides.
I worked a summer job in retail a few years back, at Canadian Tire (a popular Canadian retail chain -- think Wal-Mart meets Home Depot). You have to remember that in a busy store, employees probably have 5 different things on the go. The shipment of plumbing fixtures just arrived and your boss wants you to stack them on the shelves NOW. Meanwhile, customer 1 asks if you can help her find the light bulbs advertised in the flyer. While you are roaming the aisle looking for those, customer 2 asks if you can help him find something too. You tell him you're busy with a customer already and you'll be right with him. Meanwhile customer 3 arrives at the paint counter and pushes the "call" button so you go over and tell him you'll be right there. You hear the sound of a heavy cart rolling by as one of the warehouse guys drops off another pile of plumbing fixtures...
Now your phone rings, and it's someone calling to ask if you can check if something's in stock. Now you need to drop everything and find the nearest computer terminal to look it up. Or if they don't have the item code, you have to walk over to the stack of ABS pipe fittings and have a chat with the person on the phone. "Did you mean the 3" elbow? The black one? Hmm, I don't see any of them here, but let me write down the product code and I'll walk over to the computer to check..." Which you are happy to do, but you are already breathless from all that running around, three different people are still in the store waiting for you and giving you the evil eye, and as you look up you see your manager watching you from his office.
It's not always THAT busy but I would have a situation like a few times every day. I took this job to earn some extra dollars while writing my thesis, but I had to quit because I was coming home every day exhausted and in no condition to do any writing! It was fun in its own way, but eye opening.
To clarify: I'm not justifying rude service. If they're rude to you, report it. But understand that they might be a little frustrated, breathless, and very busy, so try to be polite and patient in return.