He hadn't 'bargained on' how his new position in the company would change the way people treated him. [=he was surprised by how his new position changed the way people treated him]
You're allowed to go to the football game tonight, but I expect you to 'keep your side of the bargain' [=do what you agreed to do] and clean your room.
They've agreed to turn the land over to the state, and the state, as its part of the 'bargain', has agreed to keep it undeveloped.
(..) You concede the necessity of goin' to school... we'll keep right on readin' the same every night... just as we always have. Is that a bargain? Therejust didn 'tseem to be... anyone oranything Atticus couldn 't explain. Though it wasn 't a talent that would arouse the admiration of ourfriends... (..)1962 To Kill a Mockingbird