When one goes on the bus – who has preferenace regarding the blind on the window. Often I put it down and then a person comes to sit in front or behind and puts it up.
In the summer, when the sun is often disturbing to passengers, the general custom (certainly on intercity buses) is to lower the blinds. This is what the blinds are made for, and therefore those who wish to lower the blinds will have the upper hand.
In general, the halachah in this matter, like the matter of opening and closing windows, depends on the general custom. Please see https://dinonline.org/2011/05/14/opening-windows-in-the-springautumn/ for further details.