How would you respond to a car buyer who makes stuff up after sale?

Sold a car to a buyer who test drove the car first. He mentioned bad struts, bad engine mounts and others which I wasn't aware of since I'm not a mechanic (he could've been lying for all I know). So I gave him a 20 percent discount. He thanked me and promised to leave a positive feedback. Well, few days... show more Sold a car to a buyer who test drove the car first. He mentioned bad struts, bad engine mounts and others which I wasn't aware of since I'm not a mechanic (he could've been lying for all I know). So I gave him a 20 percent discount. He thanked me and promised to leave a positive feedback. Well, few days later he negs me instead mentioning all the stuff that he had complained about which I had given him a discount for. He also claimed bad transmission which isn't true at all. It has a slight lag when accelerating which was mentioned in the ad.

So how would you respond to his neg? So he's complaining about stuff he already knew before buying or stuff I had mentioned in the ad. I had perfect feedback prior to this.
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