Why actually, yes, as a matter of fact if you billed medicare or their insurance for both ends of the trip requiring an ambulance then IT IS fraud. If you adjusted the documentation so that it appeared the person required an ambulance for both ends of the trip when they really didn't then IT IS fraud. Thank you for admitting that you run a fraudulent buisness with illegal billing practices.
You can attempt to justify your actions however you want and try to make yourself out to be the good guy, but the plain truth of the matter is that you, and all those who follow similar practices to you are defrauding the government, insurance companies, and individual people to line your pockets.
Good buisness plan if you can get away with it.