re: Shopping for engagement rings, educate me

I have some friends that own a jewelry store. They make ring like most. They actually let me take 3 Diamonds for 2 weeks getting appraisals. The one stipulation was never let them out of my site. so they wouldn't be switched.
They have many diamonds being sold out there that are pretty to the naked eye but have tiny specs of carbon in them. These are what you need to watch out for. Even a tiny spec brings the price down 60%-70%.
Study the diamond so well that you will be able to tell if its ever swapped.