How to moderately prep concrete floor without deep scratches

This is a medium hardness of concrete floor. The owner wants to have the old black surface removed, and re-seal the surface. Considering the surface is flat enough, after a small demo testing, 
Contractor applied our 60/80 grit trapezoid diamond grinding shoes to start. The characteristic of this grit is the diamond crystal s are finer, the segments can ideally deliver moderate and finer scratch patterns. After the application, on one hand, it can successfully grind the old sealing out, on the other hand, it won't leave deeper scratches. The process ended up with new surface exposed and left minor scratches.