We have very many approved apparitions and mystics in the Church. Though the Church does not require us to believe in private revelation. But God does intervene directly sometimes to alert mankind to come back to Him.
And of course with every genuine visionary there will be many false ones. St. John of the Cross wrote of the dangers of seeking to have visions or special gifts "... the devil causes many to believe in vain visions and false prophecies; and strives to make them presume that God and the saints are speaking with them; and they often trust their own fancy. And the devil is also accustomed, in this state, to fill them with presumption and pride, so that they become attracted by vanity and arrogance, and allow themselves to be seen engaging in outward acts which appear holy, such as raptures and other manifestations. Thus they become bold with God, and lose holy fear, which is the key and the custodian of all the virtues; and in some of these souls so many are the falsehoods and deceits which tend to multiply, and so inveterate do they grow, that it is very doubtful if such souls will return to the pure road of virtue and true spirituality."
Most of the above approved visionaries were poor, uneducated, and also suffered greatly because of the mission that God had given to them. They did not become Saints because they had witnessed apparitions or that they had extraordinary gifts, but because they lived lives of heroic virtue and holiness. They also submitted themselves completely to the authority of the Church and were totally obedient to their superiors. When 'visionaries' start giving out publicly about the Church authorities or are openly disobedient to the requests of the Parish Priest or local Bishop, they are not genuine. St. Pio was silenced for eleven years by the Church and he obeyed. And of course this showed that he was a man of genuine holiness.
The following is an excerpt from St. Fausintas Diary on the importance of obedience to the authorities in the Church....
I apologized for taking up Mother's time and left the room. At that very moment I saw Jesus standing at the kitchen door, and I said to Him, "You commanded me to ask for these mortifications, but Mother Superior will not permit them." Jesus said, I was here during your conversation with the Superior and know everything. I don't demand mortification from you, but obedience. By obedience you give great glory to Me and gain merit for yourself.
Also St. Faustina wrote "Satan can even clothe himself in a cloak of humility, but he does not know how to wear the cloak of obedience." (Diary, par. 939).
St Margaret Mary Alacoque was told by Our Lord: "Listen, My daughter, and do not lightly believe and trust every spirit, for Satan is angry and will try to deceive you. So do nothing without the approval of those who guide you. Being thus under the authority of obedience, his efforts against you will be in vain, for he has no power over the obedient" [Autobiography].