On Monday 8th August I flew BMI baby EDI-EMA as you have to pay extra for the emergency exits so they are rarely filled, after doors closed one of the PAX (not me) moved into an empty O/W exit seat only to be told by a FA that he had to get back to his alocated seat because as he had to pay extra for the seat it would be the same as if he had been moving to first class
I believe you will find that in Australia, the overwing exit rows must be occupied by at least four able-bodied persons (one for every window and aisle seat). If no one has paid the extra fee to sit there, the gate agents and/or cabin crew will look at the manifest and "upgrade" frequent fliers, tall people, whatever, to make sure these seats are filled. (This doesn't apply to exit rows in widebody jets that have cabin crew at every exit.) So maybe this country doesn't always have it all wrong?