On more than a few occasions in my 19 years as a priest, I have met an individual who has told me they have seen Jesus, Mary, some saint or so on. I have also been pulled aside by good Catholics who have seen me talk to such people and speak in hushed tones about said things and act as if somehow the person were in need of psychological help and heavy medication. I shrug my shoulders and say, "Such things are in the tradition and history of the Church." This doesn't mean I accept or believe every person who says such, but that I will allow it it to be within the realm of possibility until proven that it isn't. I'll not be one to tell God what He can or cannot do.
Certainly, that appearances have happened, messages given (locution), and such have happened is definitely part of the rich tapestry that is the Catholic faith. Think Lourdes, Fatima, LaSalette, Guadalupe, Knock and many other approved apparitions of Christ and the Blessed Mother. We believe that Mary herself was visited by the Archangel Gabriel. However not every apparition turned out to be legitimate, Bayside NY, comes to mind. In most every case the seers were discounted, thought mad, accused of blasphemy and deceit. Some were even persecuted. The Church does not discount such possibilities no more than it discounts out of hand demonic possession or the movement of the devil. In either case, criteria are used to sift the chaff from the wheat; the truth from the lies.
The Church does believe in the operation of the supernatural in human events. However, such is tested. Eliminations are made. Psychological, physiological, environmental, and mental factors are eliminated. Sometimes people do lie to get attention. Sometimes there is something psychologically wrong. Sometimes the unknown presence of environmental factors are found. These must be eliminated as factors.
So what is the the next step once these have been eliminated and something is happening. Next we must be sure of its origin, We remember that the devil is the master of deceit and will appear as an angel of light in order to cause confusion and division. We then look at the messages of these visits. Nothing of God will overturn revealed truth. The Church, and by that I mean the official Magisterium of the Church, goes through the messages and looks at their content and compares it to revealed truth. Nothing Of God will go against it, nothing of the devil will stick fully with it. That which is found wanting is condemned. Usually the Church will wait until the event has ended. It would be horrific if the Church were to declare something to be true only to have the messages take a very decided turn away from revealed truth. This is why, in so many ways, the event at Medjugorje is still not fully approved; the locutions have not ceased.
There is also the matter of the fruits born of the event. Does it lead to the greater adherence to the faith and develop our relationship with God? All apparitions of God lead us closer to God and not closer to a personality. With the rise of net, it is hard to personally sift what is what. Some will spawn conspiracy theories as to why the church didn't approve of something. Some will gain followers because of the bombast and apocalyptic feel. Me? Let's stick to what we know. We know the approved. We know that the devotional life is good. If we are on something and the site sounds like a cult of personality, it probably is and we should flee. Nothing of God will incite division within the Body of Christ. Nothing!