Engagement Ring

You know how to check one out in a jeweler's glass? The more carbon spots, the less valuable the stone. Retail prices are pretty standard. You can buy an uncut stone and have it cut a lot cheaper. Google some diamond mines and see if they have any offers on their stones. You'd be surprised at how inexpensive an uncut stone can be. You never want to buy stones that you can't hold and see first though.

Also - never buy one without a certificate of authenticity from a REPUTABLE assayor.

Pawn shops are good places to get good stones at a low price - but take that jewelers glass and make sure the company listed on the certificate is reputable.

If the stone has any yellowish tint to it, leave it there unless you are getting a fully yellow fancy diamond, but the yellow should be rich yellow in that case, not just a yellowish cast. A little bluish cast isn't bad, but try for one that lives up to the nickname "ice".

Take the stone to a window so you can look at it in REAL light. Jewelers use light that enhances stones and you need real light to see the real color of the stone.

Check the stone (in a glass) for internal or topical scratches, or filled cracks. Those lessen the strength and value of the stone. You won't see them with the naked eye but they do show in the glass.

It's extremely rare for a stone to be completely free of flaws. If it is, you might want to be concerned if it's cubic zirconia instead of a diamond. In a pricy diamond these flaws will be extremely few and very small, but they will be there.

Get at least a 3 day money-back guarantee so you can take the stone to another jeweler or an assayor to make sure you didn't get ripped.