Don't think he would send it off. Then you are taking a risk that the color and clarity are properly graded. Notice the difference in prices according to cut quality. The problem in choosing a price is that you really don't know for sure what you are buying. I second Lawmax, Price jumps with every change in the color or clarity grade.
Cut quality affects the price too.
You need to have expert opinion on this diamond. We also have no reason to question your friend integrity. We just telling you what are the right things to do in the case like yours. Many diamonds look great under bright light. The difference between ideal and overage cut will be seen under dim light, e.g. candle.