In 1 Samuel 16:4 (NASB)
So Samuel did what the Lord told him, and he came to Bethlehem. Then the elders of the city came trembling to meet him and said, “Do you come in peace?”
Why were they trembling to meet Samuel?
The story in 1 Sam 16 comes immediately after the incidents of 1 Sam 15 in which a lowly prophet denounces the King!! Recall the main points of 1 Sam 15 -
Under such circumstances, the prophet Samuel was for fearsome and had greater authority that the king!
Little wonder that when Samuel appeared anywhere after that, the people "trembled" (1 Sam 16:4)