In today's first reading (1 Samuel 3:1-10,19-20), we read about young Samuel called by God in the middle of the night. From that moment, his calling is confirmed by Eli, "and the LORD was with him, not permitting any word of his to be without effect. Thus all Israel from Dan to Beer-sheba came to know that Samuel was an accredited prophet of the LORD."
Whereas all Christians are called to be prophets, there is a particular ministry to prophecy, just as there is, according to St. Paul, a special gift of prophecy -- a charism, given by the Holy Spirit. Samuel is a recipient of this wonderful gift, and so the Lord makes sure that "any word of his" (Samuel's) is not without effect. And so everyone knows that he is an accredited prophet of the Lord.
It would be wonderful in this day and age to know for certain that certain individuals are "accredited" prophets of the Lord. Scriptural authority is ratehr limited because what is spoken by the preacher is not necessarily what is written. That is because some things that must be said are not always explicitly written, e.g., the truth about abortion and the sanctity of embryonic/fetal life. And so people find ways to dither and differ from the silence of or lack of explicitness in Scripture.
Needless to say, we do have that in the Catholic Church: our bishops and the bishop of Rome. The Orthodox have that, and they get by for the most part with just their bishops. I'm not bragging about that, but I am thankful. I don't know any of the bishops personally, nor am I familiar with any significant portion of what they have been teaching. I trust their office, however, as Apostolic successors, because I trust the one who instituted the office: Christ, the head of the Church. I also trust the one who continually confirms the office: the Holy Spirit, the soul of the Church. None of these bishops have ever been impeccable -- without sin -- but I believe in God's promises to the Apostles in particular, authority to teach. They are accredited prophets of the Lord, and I can trust that accreditation.