Reading this question reminded me of a scene in the Artemis Fowl series. In the third book, The Eternity Code, Juliet gets Holly able to enter a facility this way:
She [Holly] had got permission to enter the facility minutes earlier when Juliet had called to enquire about the public tours. Juliet had put on her best cutesy voice for the security guide.
'Hey mister, is it OK if I bring my invisible friend?'
'Sure it is, honey,' replied the guide. 'Bring your security blanket too, if it makes you happy.'
[reminder if needed: fairies can't enter a human dwelling unless invited. Whether the rule applies to dwellings or buildings is kind of debatable since this instance takes place at a lab or a facility (not a house), if my memory serves me, but let's assume for this question that it was a building which needed permission to access.]
I can see how the "security guide" has some kind of authority over the place (being a guide and all), but what would happen if someone else came along and said "No, you can't, shoo!" ? Would the previous statement from the guide be revoked?
On a bigger scale, what if the "rightful owner" of the place stated once that "no, no fairies can enter this building. Ever. And that is my final word and it should not be able to be overriden by any minion of mine." ? Would the guide not have been able to allow access in the first place (even if not knowingly)?
It's been some years since I read the books and I couldn't remember such an instance in what I read. I don't think I ever read an interview of Eoin Colfer. In the end, my question boils down to: who gets the last, irrefutable word about who can or can't enter?