Only common sense would tell you that if you are to be flying with 3 pax then you want to know what it at least feels like to be fully loaded - I dont see a reason why you cant do this and it sounds like you have been told a load of old pony. It's a shame it ended up like that with the flying school you have been with for so long, but it is your well earned money that matters and the only way to complain (and rub it in a little) would be to move next door
