The other thing that happens at least once a day is a customer comes in with a part number, extremely confident that its the part they need, I sell it to them, then two hours later they are back returning it, angry that it was the wrong part when they didn't even give me a chance to check to see if it was the right one.
Which is why I always ask, "Do you want me to double check and make sure it's the right part?"
We have over half a million parts in inventory, I don't remember every single part number and its applications.
That's why I get both sides of it. I was on the customer side for a long time, but I can see what it's like from the counter side now and understand why things are the way they are.