Our Lord already addressed this Himself:
"Not every one that saith to me, Lord, Lord, shall enter into the kingdom of heaven: but he that doth the will of my Father who is in heaven, he shall enter into the kingdom of heaven. Many will say to me in that day: Lord, Lord, have not we prophesied in thy name, and cast out devils in thy name, and done many miracles in thy name? And then will I profess unto them, I never knew you: depart from me, you that work iniquity." - St. Matt. 7:21-23
"Then if any man shall say to you: Lo here is Christ, or there, do not believe him. For there shall arise false Christs and false prophets, and shall shew great signs and wonders, insomuch as to deceive (if possible) even the elect. Behold I have told it to you, beforehand." - St. Matt. 24:23-25
Furthermore, St. John of the Cross is one who strongly advised against seeking visions and locutions because of the strong possibility for deception by Satan. He said it was better to ignore all those, rather than believe they were from God.