JOEL - God can manifest Himself to His prophets in different ways. He can physically appear to them in a vision, as He did with Moses(Ex. 33:11, Deut. 34), Enoch (Moses 7:4), and Joseph Smith (Joseph Smith History 1:17); He can speak to their minds as He did with Elijah(1 Kgs. 19:12-13); or He can relate His will through dreams(Joel 2:28). An appearance of God to any of the prophets would be an extremely personal and sacred thing; something they would not desecrate by announcing it to the world, unless the reason for the visit was to reveal some new or important doctrine that God wants us to follow(Amos 3:7). Most Biblical and latter-day prophets probably have not had a direct visitation from God, including President Hinckley(my opinion). But they have all received visions, revelations, and inspiration from Him for running the affairs of His kingdom on earth. As proof of their prophetic calling we must look to the fruits of their work(Matt 7:16, 20); the fulfillment of their prophecies(Deut. 18:22); confirmation of their divine calling from the Holy Ghost through prayer(James 1:5-6); and we should exercise some faith that they are being directed by God, by following their counsel and enjoying the promised blessings(D&C 82:10).