If only it were that simple. Many developers forget to add the airport marker and the star won’t show in the world map without the marker (it only shows up if you zoom in really close). Moorea and Motu Mute were around for months without any easy-to-find evidence that a purchased airport was there. Now they have a marker and a star visible from high above the Earth thanks to their inclusion in World Update XIII, but if anyone bought the Pearl Simulations versions of these airports and forgot they had them (which is easy given the world map showed just a tiny dot), they now have two copies of both these airports - and no way to tell that they have multiples until they fly there and see scenery colliding (if they get that far without crashing the sim).
And the problem is not confined to 3rd party developers. LSZN (Hausen am Albis) has no airport marker that shows up until you zoom in really close, so no star that’s easily visible (even though we all own it). So no easy way to tell that Microsoft has a hand-crafted airport there. It’s the same with TNCM (Princess Juliana St. Martin). Check it out - go to the world map and see how difficult it is to find these markers without doing an actual search for their ICAO code - you have to be REALLY close.
Sure, if you diligently look up the ICAO code on the world map before buying an airport, this won’t be an issue. Buy I guarantee the vast majority of people don’t do that. The point is, it’s really easy to miss the fact that you have certain airports, which is why I think there should be a warning when you’re trying to purchase an airport you already own. And there should be some way to run a check to see if you have any conflicting airports.