To have an ulterior motive or hidden agenda.
用心居心，打算。心中另有算计。指言论或行动另有不可告人的企图。
清·吴趼人《二十年目睹之怪现状》第九十九回王太尊也是说他办事可靠，那里知道他是别有用心的呢。”
His flattery seemed genuine, but I suspected he had an ulterior motive.
Learn the next connected idiom: 别有用心 (bié yǒu yòng xīn) → 心有余悸 (xīn yǒu yú jì)
Want to explore more random idioms? Try our 🎲 Chinese Idiom Generator