Daily Chinese Idiom Guessing Game
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.