I sold cars for five years and now train sales consultants.
Everybody lies.
Buyers are liars.
Buying a car is SCARY for folks. it's the most expensive thing most people will ever buy. They are terrified.
Also, in this age of 5,000 different picker and house hunting and car buying shows on cable television, everybody has been trained to haggle and low ball.
With a specialty item like a decade old, generally unloved model Porsche, you just have to exclude average folks and list your car on Porsche specific sites and only deal with "True Believers" who know what the car is about.
Dealing with the public in retail sales is THE most annoying job on the planet.
It's not for the faint of heart.
Watch "Glen Gary Glenn Ross" sometime for the sales meeting with Alec Baldwin.