It's a deal.
You will need to pile 6 inch concrete blocks around to get correct height.
Maybe ten or fifteen.
There is no other way, don't let anyone tell you different unless they have paid someone else to fill at least a hundred lots like I have.
Sticks to show height get knocked over.
Even blocks get pushed down by wheelbarrows rolling over them.
No human can tell by eye when you reach six inches, including me.
Hope it rains during the week they fill. It will lower the sand height 25%unevenly.
Don't pay in advance for sand because you trust them. They may be frustrated by many factors during the job and find themselves in a conflict because you prepaid.
This unfortunate dispute with someone you otherwise like will be your fault because you prepaid.