Focus on value. You’ll get a lot more bang for your extra bucks by buying an ideal-cut diamond. But if you can’t otherwise discern differences in quality between two stones, don’t pay more for the higher-quality stone. Most shoppers should avoid paying extra for diamonds with color grades above F or with clarity scores better than SI1.

Stick with GIA-certified stones. If the store can tell you only that a diamond is “certified,” without a designation from the GIA or other reputable organization, ask to see something else. Many other certifications tell you nothing about stone quality.

Compare prices. You’ll find huge store-to-store price differences for comparable diamonds. When our undercover shoppers obtained price quotes from local stores and chains for excellent cut round brilliant diamonds, weighing 1.50–1.55 carats, VS1 or VS2, G or H color, some stores offered prices of $19,356 or more while others charged $11,500 or less. Prices available from online-only sellers were even lower.

Look at loose stones. Some stores pre-set lousy diamonds to hide flaws.

Consider alternatives. Sapphires, rubies, and other stones offer similar dazzle at significantly lower prices. Lab-grown diamonds are chemically and physically identical to mined diamonds but cost about 20 to 30 percent less.

Review the return policy. Buy from stores that offer returns with a full refund within 30 days. And pay by credit card. If a store doesn’t come through, you’ll have the option of disputing the charge with your credit card company.

Get expensive purchases appraised. Although you’ll have to pay about $50 to $200 for an appraisal, it’s good insurance against being given—either intentionally or by mistake—a switched-out gem that’s of lower quality than what you paid for.