As a rule second cars like the Z4 can have more owners with less detriment, as people do tend to buy and sell them, however mainstream and newer cars it can decimate the value due to worries about it being a lemon, why sold, etc.
I purchased a 1 owner Jag XF at 12 months old and later found out it had 4 previous owners and I was the 5th !!!
After some argument the dealer who had lied, took it back. I had been advised that the value was at least £10k lower than a one owner car with me the second (which I now have)