I guess what you have to do is do some online research on what makes one type/cut of diamond more valuable than the others..Make sure you go and check around in some reputed stores,,ask them for the technical details..Make sure you look at them under microsope ro clarity and blemishes,,,they have serial numbers etched in them,,,that should tally with the certificate you get,,or else that certificate is not going to be worth more than just a piece of paper..You will find out about it yourself more than anyone can educate you with this experience. ( you will probably end up with gift vouchers worthing 100's of $$ (which of course is just like a bait to lure you back to the store,,and 100$ cannot buy anything in those stores)..

Anyways buying diamond ring for engagement is like attaracting a girl because a guy has a new corvette or a slick sports car,, After all is done the ring stays nothing more than a good memory,.,It's like the girl that got attracted to you because of your corvette does not want you to drive it,, but wants you to go around in a family van after getting married,,