One strategy is to scan for the phrases you know and underline the key words. For example,
A. Hand him back his laptop and refuse to do business
A customer is insisting that you upgrade his laptop video card's RAM from DDR to Graphic-DDR. After a few attempts to explain to him that video RAM is not upgradeable, he pulls an ancient PCI video card out of his pocket showing you places where RAM can be added, goes through a long speech about the how he used to add RAM to his desktop's video card "back in the day," then accuses you of lying to him. You should:
B. Pull the video card out of his laptop and show him that there's no place to upgrade RAM.
C. Go to a manufacturer's website and show him no one gives upgrade options.
D. Calmly and without taking it persomally tell him he's wrong.
Hope that helps some.