Sold one's soul is an expression used when someone does something morally reprehensible in exchange for personal gain or advantage. However, there are several synonyms that can be used to convey the same meaning. The phrase "made a deal with the devil" is a common synonym, implying that the person has made a pact with a figurative devil to achieve their goals. Another synonym is "crossed the line," suggesting that the person has gone beyond the boundaries of what is considered acceptable. "Compromised one's integrity" is yet another expression that can be used to refer to someone who has gone against their principles or values for personal gain. Regardless of the synonym used, the underlying message remains the same.