Buying a diamond, particularly for an engagement ring, is a complex process. There are many factors that make for a “good” diamond. Many places now are offering online diamond purchases. This is quite a risky process. Even as a professional, due to the risks, I choose not to buy diamonds either online or from overseas suppliers. If I can’t return the diamond if I find it unacceptable, I won’t buy it. In my experience, all too often a diamond is either verbally, or via a certificate described as being a “good” stone, only to receive it and find otherwise. Then there is the risk of not receiving it at all.
Buying a diamond from a professional who can offer for you to view the stone prior to committing to it, may not be the cheapest method, but if they are honest and genuine in their dealing with you, it will make for a good quality, beautiful stone for the rest of your life.