It happens on occasion, yes. To be honest given the cost of a cab it is much better on your blood pressure to just suck it up and forget it rather than chase your tail to try to collect $20. I know that it is a principle thing and you have paid for the service, etc., but life is too short. My personal rule is that if the car is more than 5 minutes late I call a cab and keep moving. The only time it really caused a problem was one New Years Eve at around 11:45 PM where it was tough to get a cab when Emirates' car did not show up. The funny thing is that I then sometimes get a call from the car service when I am already in the cab on the way to the airport asking where I am as the car is waiting for me BUT I am in a totally relaxed state of mind and rather enjoy telling them that I have set off under my own steam.