Adam Clarke on 1 Samuel 27:12

He hath made his people - utterly to abhor him - This deception, which Dr. Delaney says "did harm to nobody, and to the account of which he is at an utter loss what degree of guilt to charge," imposed upon Achish, had the most direct tendency to make him imagine himself secure, while in the utmost danger; and to have a faithful friend and able ally in David, while he was the veriest enemy he could possibly have. Shame on him who becomes the apologist of such conduct! As to Dr. Chandler, he should know that no lie is of the truth, and that all falsity is an abomination to the Lord.