Blue Nile and other online stores offer great prices because there is no guarantee they are selling what they say they are.
I must preface this by saying I am no expert, I have just spent a lot of time with a wholesale jeweler, with over 30 years in the business, who happens to supply well over 16,000 shops with their diamonds.
It works like this. All diamonds when they come in are immediately and automatically grouped into a broad category of the 4 C's and then are put into a cache of similar diamonds before they are sold. The certificates are pre-determined and the diamonds that most closely fit the certifications are given to them. The diamonds will appear to be what they say they are to an untrained person (you or I) but a true jeweler will tell you that most of these diamonds are far from what they claim them to be.
Ask the jeweler to see the chart that they have for determining retail prices. It is called the Rapaport (I believe), a quarterly report put out by the diamond authority that determines retail price. A lot of them will choose not to show it to you and rather punch in a whole bunch of numbers to a calculator and then show you a huge number and then say something like "And you get a special 60% off discount" and hit a few more keys and show you a final price. All retail prices are more or less predetermined based on the 4 C's, but it is no where near what the whole sale price is, so haggle, haggle, haggle.
If you are buying loose, put them all on the table next to one another and look at them with the jewelers magnifying glass. If you can't see the differences, go with the best looking and cheapest diamond. A friend of mine put two diamonds right next to each other with a $2000 difference and couldn't see the difference, and clearly chose the cheaper option.
I do like the option of buying loose because you can make it into the perfect piece of jewelry for your future fiance. I had a basic idea of what she wanted (3 stone, not a plain band, and round cuts) and worked my way backwards by picking out a ring style and then the diamonds to fit in it based on my price range.
Oh and metal. If you are looking for something with the silver color, skip white gold and platinum. White gold is essentially bleached yellow gold and will always turn increasingly yellow over time. Platinum is very nice, but expensive and scratches easily. Try paladium, it is whiter and brighter than white gold and will not scratch near as easy as platinum and the price is less than half of platinum and only slightly more expensive than gold. Some jewelers do not use this metal, but it is on the periodic table and is a precious metal just like the other two.
If any of this doesn't make sense feel free to PM or ask any clarification questions. Hope this helped and I don't seem like a complete moron with endless drivel.
Best of luck with the purchase
