An engagement ring is not an everyday purchase and the selection of a diamond seems complicated at first. Therefore, many choose to not search further and just buy a "finished" ring at a high street retailer.

By doing so, you may find a beautiful ring... but it will most probably be overpriced.

Buying online is 30 to 40% cheaper than buying in a physical store - for the exact same quality.

MORE: A comparison: Buying an engagement ring online vs offline

The GIA gives each diamond a color grade starting from "D" (colorless - i.e. extremely white) and going all the way to "Z" (yellow). We, at My Diamond Ring, sell diamonds from the color "D" to "M" (faint yellow).

For engagement rings, white being the most desirable color, most buyers make the common "mistake" of wanting a "D" diamond only.

D diamonds are the most expensive ones. Slightly lower color grades can look just as white to the naked eye while being drastically cheaper.

BUYING TIP: Go for a "G", "H", or "I" color diamond instead.

EXPERT TIP: If you choose an even lower color grade ("J" to "M"), you can make it appear whiter by setting it into a yellow or pink gold ring.

For some people, the bigger the stone the better! But a big diamond - i.e. with a high carat weight - is not the only parameter to take into consideration. Anyone in search of a diamond is limited by his budget. If you buy the biggest possible diamond for your budget, you may regret its overall quality...

We suggest searching for a "good enough" quality diamond and choosing the biggest diamond you can afford in that quality range.

LEARN MORE: Diamond Buying Guide - how to get the biggest possible diamond for your budget

Every diamond is unique and impurities - also called "inclusions" - also contribute to a diamond´s distinctiveness. The most valuable diamonds have an "internally flawless" (IF) clarity grade, meaning that they show no carbon inclusions whatsoever. Such diamonds are not only extremely rare but are also extremely expensive.

No one will look at your diamond with a microscope. There is no need to go for an "internally flawless" (IF) or "flawless" (F) diamond.

BUYING TIP: A very slightly included diamond ("VS1" or "VS2") is sufficient and will look pure enough to the naked eye! Even diamonds with purity grade SI (light impurities) are hardly visible to the naked eye.

When buying a diamond ring you should always insist on the certificate of the diamond. Ideally, the diamond you are buying should be certified by the GIA - the most relevant and respected grading institute in the world.

Only then you can:

• be sure of the ethical origin of the stone
• make sure that the quality characteristics indicated are correct.

MORE: Why do I need a diamond certificate?