Solved

Contract negotiations

I read that contracts can be negotiated (meaning, you can bargain with the drivers, the staff, the suppliers the salaries/supplies). How can it be done? Because when I hire someone or change suppliers, I don't see anywhere an option to do so

This was possible in the game's old format but the feature does not exist anymore. (new format began August 2016)

Ok. Arigatou very much for the answer! :)

You're welcome!