As a potential buyer, my feedback on this advert is as follows.
IMO.
I don't think it is cheap, it is priced about right to sell in a normal selling time frame considering it doesn't have Nav. Cars can take a few months to shift. the Z is a niche car, and also not having Nav will limits the market further. I bet if you fit nav, then it will sell the next day, or drop the price further to attract someone that would of otherwise waited for a car with Nav and low mileage.
Personally if I was selling this, I would start another ad. Put a range of pics in that include the inside, under the bonnet etc, find out what the optional extra's are and list those clearly. I would not be putting German descriptions in either to confuse matters more. (look at some cars that have sold fast on here and copy the add format basically)
The car looks nice, and has a good spec, also list out the service history clearly with dates, including where they were done. All this should be in the same post and not spread across several pages.
Just trying to help