Is flattery that involves lying unlawful (haram), and how do we deal with it, and what should we do if the flattered person asks for an opinion on an unlawful act?

Lying is forbidden and reprehensible, even in jest, based on the Prophet's (peace and blessings be upon him) saying: "I guarantee a house in the middle of Paradise for one who abandons lying, even if he is joking." A Muslim must strive for truthfulness and avoid lying. If one needs to be polite, they should use allusions (ma'areedh) and circumlocution (tawriyah). As for politeness in forbidden matters, it is not part of a Muslim's character; rather, they must clarify the truth, deter from falsehood, enjoin good, and forbid evil, based on the Prophet's (peace and blessings be upon him) saying: "Whoever among you sees an evil, let him change it with his hand; if he is unable, then with his tongue; if he is unable, then with his heart—and that is the weakest of faith."