Albert Barnes Commentary 1 Samuel 12:3

"Here I am: witness against me before Jehovah, and before his anointed: whose ox have I taken? or whose ass have I taken? or whom have I defrauded? whom have I oppressed? or of whose hand have I taken a ransom to blind mine eyes therewith? and I will restore it you." — 1 Samuel 12:3 (ASV)

His anointed: This refers to King Saul. Although the title "Messiah," meaning "anointed" (from the Greek Christos), had previously been given to the High Priests (Leviticus 4:3; compare to 1 Samuel 2:10, 35), this is the earliest instance of an actual king of Israel bearing the title of God’s Christ and thus typifying the true Messiah or Christ of God.

Any bribe: Literally, this means a "ransom"—the fine a criminal paid instead of facing imprisonment or death (Exodus 21:30). The term was also applied to the bribe paid to an unjust judge to induce him to acquit the guilty .

To blind...: This expression refers to someone who averts their eyes, whether to refuse assistance, show contempt, or, as in this context, to wink at what is wrong.