Peace if possible, truth at all costs.
Is manipulation a sin? Yes, manipulation IS a sin. Allowing people to control and manipulate you in a relationship is also a sin because it is a form of idolatry. If someone is trying to manipulate and control you tell them to get out of your face.
It's also stealing. Stealing someone's trust to benefit in some way.
Enter his gates with thanksgiving and his courts with praise; give thanks to him and praise his name. For the Lord is good and his love endures forever; his faithfulness continues through all generations.
Psalm 100:4-5 NIV
Who is wise and understanding among you? Let them show it by their good life, by deeds done in the humility that comes from wisdom. But if you harbor bitter envy and selfish ambition in your hearts, do not boast about it or deny the truth. Such “wisdom” does not come down from heaven but is earthly, unspiritual, demonic. For where you have envy and selfish ambition, there you find disorder and every evil practice. But the wisdom that comes from heaven is first of all pure; then peace-loving, considerate, submissive, full of mercy and good fruit, impartial and sincere. Peacemakers who sow in peace reap a harvest of righteousness.
But what does it say? “The word is near you; it is in your mouth and in your heart,” that is, the message concerning faith that we proclaim: If you declare with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you profess your faith and are saved. As Scripture says, “Anyone who believes in him will never be put to shame.” For there is no difference between Jew and Gentile—the same Lord is Lord of all and richly blesses all who call on him, for, “Everyone who calls on the name of the Lord will be saved.”
Romans 10:8-13 NIV
Therefore you have no excuse, O man, every one of you who judges. For in passing judgment on another you condemn yourself, because you, the judge, practice the very same things. We know that the judgment of God rightly falls on those who practice such things. Do you suppose, O man—you who judge those who practice such things and yet do them yourself—that you will escape the judgment of God? Or do you presume on the riches of his kindness and forbearance and patience, not knowing that God’s kindness is meant to lead you to repentance? But because of your hard and impenitent heart you are storing up wrath for yourself on the day of wrath when God’s righteous judgment will be revealed. to those who by patience in well-doing seek for glory and honor and immortality, he will give eternal life; but for those who are self-seeking and do not obey the truth, but obey unrighteousness, there will be wrath and fury. There will be tribulation and distress for every human being who does evil, the Jew first and also the Greek, but glory and honor and peace for everyone who does good, the Jew first and also the Greek. For God shows no partiality.
Romans 2:1-5, 7-11 ESV