I don't think that one can say "I would only take this clarity or this color" because you can find a stone within those specs and it may not look half as nice when compared with an SI3, D color in the same size range. You really have to look at the stone.
The issue with clarity/color when getting into 3+ carat stones is that One notch up or down in color or clarity can mean $10-30,000. People are very likely to "fudge".
The Jewelry Store can take a non-cert'd diamond:
GIA would call it:
4.03, SI2, I color Excellent Cut and the stone would be $72,900
EGl might call it:
4.03, SI1 (VS2 even), G color, Excellent Cut and the stone at those stats would be closer to $80-85,000.
The Jeweler will than say "This 4.03ct Round is a great buy for a VS2-SI1. But there is a big difference between VS2 and SI2 on a 4 ct stone.