I understand the buyer, generally. With home repairs, you don't want to throw good money after bad. If it's an old roof, better to replace it and get a warranty than to sink money into fixing it for an uncertain time-frame with no guarantee. One of the properties I bought had roofing issues that would have cost $1000 to fix. The independent inspector told me I could get up to seven years out of the repairs, but there was no guarantee that the roof wasn't going to spring more leaks in those seven years because it the roof was overall in bad shape. In the end, I decided to spend $5000 on a new roof with a 12-year guarantee and a 25-year life expectancy. If something is just old and not having issues, that's one thing. If it's old and having issues, I generally believe in replace v. repair.
This particular house had a roof, HVAC, and water heater that were all at or beyond any reasonable life expectancy, plus a few other minor issues. None of these were disclosed. I negotiated a $13k credit, which is what I thought it would take for me to replace those items, and I didn't budge. It was take it or leave it, and I was prepared to walk away. The sellers didn't like it, but I got what I wanted. As others have said, they became legally obligated to disclose the issues I found. And once they disclosed those issues, any other buyer would have started deducting money from the purchase price. If they had disclosed the age of these issues on the mandatory disclosure form, that would have been a different story.
Back to the issue at hand.... is one potential solution to credit the buyer $7100 ($9100 v. the 2000 he is chipping in), so that you can be done with it and not bear the risk? Personally, I would never -- and my two best real estate agent friends agree -- let any seller do repairs. They have no incentive to get it right and every incentive to keep the cost as low as possible, even when it comes with a large quality tradeoff. I made this mistake once as a seller - I made quality repairs, but the buyer expected gold-plated ones, apparently. Never again. Whether buying or selling, accept as-is, negotiate a cash credit or price reduction, or walk away.