Does it matter who I buy a diamond from?

Absolutely. A company's reputation, return policy, after-sale service and trade-up policy are all crucial:

Reputation

If you've spent time on this site, you realize that there are a tremendous number of mistakes you can make when buying a diamond. While a company's good reputation won't guarantee that you're buying the right diamond for your needs, it can eliminate the issues of outright fraud or misrepresentation.

Generally, a company that has been in business for years with thousands of satisfied customers is a good bet. However, you shouldn't simply rely on a "Since 19XX" line of text in an advertisement. Talk to people who have done business with the store and find out if they're completely satisfied. Also contact your local Better Business Bureau to see if there are unresolved complaints.

Keep in mind also that even if you find a company that you trust, you should always have a qualified expert confirm that the grading report matches the diamond it represents.

Returns

Any establishment that will not give a full-money-back refund after a fair amount of time (at least two weeks) should be a warning sign. Why wouldn't they want their own merchandise back? Make sure you can get the full purchase price of the diamond back in the method you paid, not just in store credit.

Service

The diamond ring you purchase will need to be serviced for a lifetime: Diamonds must be continuously cleaned to display the greatest sparkle, ring prongs must be tightened to protect the diamond from falling out, the platinum or gold setting will need to be buffed and ring sizes can change over time.

You must find a company you can trust to make all of these adjustments for you. Generally, the company that sells you your diamond has the greatest vested interest in servicing it for you.

Keep in mind also that when servicing your diamond, unscrupulous establishments could possibly switch your diamond with a diamond simulant or diamond synthetic.

Upgrades

Some people develop an emotional attachment to a diamond and want to keep it forever. Others use special events, such as anniversaries or birthdays, to upgrade or "trade up" their diamond for a bigger or better-quality diamond.

If you think you might be interested in this in the future, make sure you shop at a store that offers a good trade-up policy. Keep in mind that if the store's policy is to give you the original price of the diamond back toward a new diamond purchase, the underlying value of the original diamond might have changed, making this more or less attractive. However, it's rare that you could get the diamond purchased back at "market." Of course, the store must be in business when you go to trade up, so make sure you're dealing with a reputable company.