While only mentioned sparingly in Scripture, Apollos was a key figure in the early church. When first introduced in Acts 18, he was “an eloquent man and mighty in the Scriptures” (18:24). Not only that, “this man had been instructed in the way of the Lord” (18:25). Notice that he was “mighty” (dunatos: able, competent, powerful) in the Scriptures, and he had been taught in “the” (definitive article emphasizing singularity) “way of the Lord.” Aquila and Priscilla heard him preaching and realized that, while he was mostly right in what he was saying, he was not completely right. So, what did they do? Did they decide “mostly 
right” is “good enough”? Did they consider all the good he was doing and conclude that it was not their business to interfere?
“They took him aside and explained to him the way of God more accurately” (18:26). They knew that being mostly right was not the same as being right. They knew that his hearers could not be taught wrong and then baptized (obey) right. He was an educated man and powerful in his knowledge and influence, but they did not let that deter them from teaching the truth!