Only if the OTHER flour mills colluded with you to do the same.
I don’t think you have to collude for people to do the same, obvious thing. Let’s say you are a hospital administrator and almost all of your physicians are under contract to you but there are specialties you can’t fill in house. You let some outside specialists “cover” your hospital in their specialty. Even if they are “under contract” elsewhere you “subcontract” at a higher rate. That hospital agrees because they know the specialists will be compensated at a higher rate for the additional stress of daily travel to a distant site for a fraction of your day.
So it’s entirely understandable how people can be compensated at a higher rate for part of their day. There are a number of situations in health care where the price varies that has nothing to do with bad faith.