When you buy a polished diamond with an accurate lab report, and you have taken your time to examine the stone thoroughly, there is little or no risk in the purchase. On the other hand, suppose you are looking at a large piece of rough and you must determine the outcome of its finished weight, shape, color, clarity, and proportions, before you can make an offer on it. Ten different buyers may well come up with ten different sets of grading data where this is concerned. Rough is not like buying a common commodity that has a set price everyone is aware of. For the true experts, it is an opportunity to test their creativity, and their sense of valuation of the potential gem. The cutter has the option of manipulating almost every characteristic of the finished stone. You are probably wondering how a cutter could change the natural state of the diamond as to color and clarity. The finished weight can also be drastically different from one cutter/buyer to the next.