Most people overspend on jewelry. And diamonds are probably the most marked-up gems. Diamond prices are usually negotiable, even if you are shopping at major chains like Zales and Kay Jewelers. “So while it’s important to know the four C’s of diamonds — carat, color, clarity and cut — the biggest lesson you can learn is to haggle. If your local jeweler or national retailer won’t come down on price, they’ll often be willing to upgrade the setting for a discount or even free,” reports MSN Money.