Test drive a Mercedes Benz

So I currently drive a c class and before I bought this car moving from BMW to Mercedes Benz they allowed me to test drive a similar car from a Friday morning and returned it by Monday lunch time, this giving me the opportunity to get a proper feel to spend , at the time , R**** cash purchase, on a car. Now I want to buy a R850k car, cash but don't give a proper answer on test drive duration. I am rather disappointed as BMW also don't get back to a person. Who will spend nearly one million rand on a car they will drive for 3 to 4 years of you probably allowed a 20 to 30 min test drive?