My experience at the IKEA loading bay is that one person will wait with the cart next to a loading bay (normally you need to choose wisely here so you get one that will likely be vacated soon, if not already). The other person will then retrieve the car and park at the bay they know where the other person is waiting and load up.
However today I was a bit annoyed when someone else took the bay where my wife was already waiting and needed to move to another spot and shift the cart over as well. What made it worse was that the person who took the spot only had a handful of items that a most people would be able to easily carry to the car.
I suspect I'll be in the minority here and most people will suggest it's just first come first served but curious to see how different opinions are.
That said I don't know how people manage alone, if the cart is just left unattended (which sounds a bit dodgy) and they take whichever bay is available - also that at the airport pickup it's more like first come first served.
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