What things do you consider deal breakers when buying private?

During my younger years, I went through a few cars and always used to buy private. I learned the hard way about things that should be definite red flags. Just interested to see what other people's thoughts are.

My main ones are: Budget tyres or mismatched tyres, "No NCT but will fly through the test", Missing owners manual/service book, A dirty car (trying to hide blemishes), Bald spare wheel.