How to Go about Examining a Diamond before Buying it?

Under a Microscope

If you get a studded ring or a loose diamond placed under a stereo binocular microscope for your perusal, do not pass that up at any cost. This would at least be a great experience even if you decide not to buy.

10x Magnification

This is the industry standard and came to be used as a result of the Clarity Rating Scale, which too is a common standard these days in jewelry sales.

Lighting

When examining a diamond, the lighting it is under can affect the way in which it appears. For example, a laboratory light would remove all color except for what the stone actually possesses. This is why you would need to view it under different light sources to determine whether it has what you are looking for.

Check for any problem with clarity, because that is where magnification helps the most. See if there are internal markings that make the stone look bad in any way.