I sold a car via gumtree last year. I met them in a neutral location and sat in the back when they took it for a test drive, I took my sister with me as felt that being a lone female it was probably unsafe to go alone. I was upfront about issues with the 10 year old car, but they still tried to make me pay for repairs after they bought it, in cash. I refused, it was a father & son tag-team, the son played the innocent youth card and the dad tried guilting me with “I thought you were a decent person, you seemed honest, if you were a good person you’d be helping him out, now he has no money and a car he can’t drive”.
Only because of previous posts on here did I have the nerve to stick to my guns, sold as seen, you knew the issues, they were present in the test drive, I was with you. You drove it away, it is yours. The issue did not make it undriveable, that is their choice.
I felt really bad about it, they did a good job and others may have cracked, but I stuck to it, especially as when I suggested they get a second quote they told me they trust this guy, I said I don’t, end of.
So, good luck and if they do try it on stick to your guns. 🙂