Oh shit, I feel your pain. I tried selling my wife's car a few years ago on eBay, and had this hag test drive it and critique every damn thing.
She tried to tell me the car was leaking something when it was clearly water dripping from the AC. She put the car in a lower gear (deliberately) and tried to act like the transmission had a problem. The car was a convertible and she sat her big ass in the back seat and asked me to put the top down. Well of course the top bumped her big ass head and it set the sensors off, and it took multiple attempts to get the top to go down correctly. But that didn't stop her from acting like the top was jacked up too.
She still made me a lowball offer, which I didn't accept. Then she texted me a few days later asking when we can finalize the deal, still thinking I would accept her offer. I firmly reminded her it was my price or no deal.
Turns outs she headed up an auto repair department at a community college. Bitch was trying to get a good used car way under book value, then have her students tune/repair/detail it for free.