Cheat Sheet | Diamonds

Men aren't known for their shopping prowess. But as we enter engagement season--from Thanksgiving to Valentine's Day--many will make the most important purchase of their lives. How to keep from getting ripped off? First, learn the "four Cs." (Hint: color, clarity, cut and carat.) But, Tip Sheet's Katherine Stroup explains, that's just the beginning:

The Jeweler: "At Tiffany, you're paying a lot for that little blue box," warns Carley Roney of theknot.com. The name does win bragging rights, but that stone would cost much less from an independent jeweler. Ask around, or go to Jewelers of America (jewelers.org) for a list. Then check with the Better Business Bureau.

The Rock: You want a loose stone certified by the American Gem Society or the Gemological Institute of America. (Rings look pretty, but you can't inspect the diamond.) Round-cut stones sparkle more, but pear- and marquise-shaped diamonds look bigger. Ask to see your picks under a microscope, not just the jeweler's loupe.

The Setting: First decide between gold or platinum. Consider matching your girlfriend's other jewelry. Platinum is the most popular, but bear in mind, gold is perfect for masking the yellowish tint of a cheaper diamond. The inside of the band should be stamped with the maker's name and type of metal.

The Price: Negotiate! Start by offering half the asking price, says Fred Cuellar, author of "How to Buy a Diamond." Look for bargains near size cutoffs: a 0.9-carat rock is $1,000 cheaper than an imperceptibly larger one-carat stone. For reference, Bridal Guide says the average couple spends $3,000.

The Safety Net: Once you have the ring, get it appraised immediately by a certified gemologist--call the National Association of Jewelry Appraisers, (410) 897-0889. Then you must get it insured, usually as a rider to your homeowner's policy. Finally, sit back, relax and pray you don't screw up the proposal.