I work in a big box home improvement store, and like any other retailer that uses lift equipment on the sales floor, when pulling merchandise from (or putting into) the overhead, we're required to have the adjacent aisle closed off. While there's only a slim chance that something would get knocked out of the overhead into the adjacent aisle, we'd really prefer that the aisle be empty if that happens. Broken merchandise is replaceable, after all.
Anyway, I'm spotting because someone is pulling a pallet of tile down from the overhead. Spotting requires me to watch the adjacent aisle, while the lift operator watches the aisle he's working on. I'm facing the aisle and the main aisle is perpendicular to the aisle I'm facing. A customer walks behind me and says (presumably with a smug look on his face) "I guess you don't want us to shop here."
I can't turn around to talk to him because I have to keep my eye on the aisle, but I do reply to him: "Sorry, sir, but when we're using lift equipment, we're required to close off the adjacent aisle for safety reasons."
I then glance over and see him walking down the main aisle with his back to me, shaking his head. A couple of minutes later, I see him talking to another associate. I can't hear what he's saying but he was gesturing towards the blocked-off aisle and he looked upset.
A few minutes later, after we had finished in the aisle, he was shopping for something in the aisle in question. I passed by him and passed up the opportunity to give him a really sarcastic "Thank you for your patience, sir."
TL;DR: Customer gets upset because safety policies require us to close off aisles when using lift equipment, so he has to wait 2-3 more minutes before getting his product.