I used to work in an electronics place, and we had a guy who came in once who wanted a specific camera at a very specific price. As in, he came in and flat-out said "I want this and I will give you exactly this amount for it." The price he had in mind was about $10 below our cost, which we told him, and he absolutely refused to budge on it, and also wouldn't just leave. Me and the manager literally had to show him the thing on the cashier screen that showed our cost and stuff and the managers was like "If we sell you this, it's like we're paying you $10 to take this camera from us."

He eventually left without it, but it took forever.