Completely wrong in fact! Yes I will probably buy from them in future and have bought many cars in the past. I have a 335d and an X5 so either of my test drives are relevant
Salesman thanked me for taking the car out and in fact was apologising for being cheeky and asking me if I wanted the car for a day.
Demo cars are to let people try and it's all about setting up possible future sales. Depends I guess on the relationship you have with your dealer.