Being insulting in Great Debates is not a good way to encourage useful discussion, (as well as being a cheap ticket off the SDMB if you insist on taking it too far).
The question has been answered multiple times by multiple posters in several different ways:
It might be a hoax;
It might be a delusion.
No one can “know” that the appearances, (if they occurred), are actually those of the BVM because:
we do not know that there was actually an appearance (as opposed to a trick of light or simply doctored photgraphs and news events);
we do not know that the appearance was of Mary.
If you happen to find yourself in a place and time where Mary (or anyone else) appears to you, you will have to make your own judgment as to whether you actually saw something or suffered a delusion and, if you did see something, whether it was really a messenger from God, a messenger from the devil, or a practical joke from space aliens. There is no way to “know” whether an apparition is of any particular being–particularly a being whom no one living has ever seen or described.