I was wondering if someone was unworthy to get a higher ranking in the priesthood, and he didn’t tell anyone, would that person receive the higher authority?
I don’t know of anyone who would be considered completely worthy in all regards to receive the holy priesthood. However, there are basic minimum worthiness criteria for being ordained to the priesthood. Let’s take as a case in point just one item, say, compliance with the Word of Wisdom. Let’s say that the candidate did not keep the Word of Wisdom, and in the worthiness interview he lied about his non-compliance. So he would be ordained, although unworthy. There are cases where the Lord would intervene, and his deception would be brought to light. But there are other circumstances where the Lord would remain silent, and let the scene play out, and the person would be ordained. Now, there are two aspects to exercising the priesthood. One is to perform official ordinances, and the other is to use the power of the priesthood in the name of the Lord. Let’s say that the unworthy priesthood holder was asked to baptize his son. Would the baptism be valid? Of course it would. He held the priesthood and performed an official act in that capacity. The act is valid. Now let’s say that the unworthy person attempted to use the priesthood power in healing the sick. Would his administration have any effect? Not any. He has no priesthood power, he has only priesthood authority.