Nasty. Just can’t trust private sellers. Nor can you trust main dealers either:
My 1st Z4 was brand new and had a leak from the very beginning. 6 months of failing to fix (and arguing) and they replaced it for another new one, but left a bitter taste.
My current z4 is a 2011 model and I got it last year, problems with brakes that the dealer tried to hide. They replaced all breaks eventually but tried to pull a fast one.
Hope your new one is all ok and you can enjoy it.