The inspector is just making a recommendation. If the buyers really want the house, they will be willing to overlook the grounding issue. You might negotiate to take $50-100 off the selling price, so they can fix it themselves. (Then they can rip up the walls.) Tell them it's in the interest of time, and that it allows them to make sure the job gets done the way they want it done.
If there are other issues, bundle them all together (i.e. don't say, "$50 for outlet, $400 for leak in roof, $100 for water in basement." Say, "$400 allowance to fix all problems.")