I've once worked for a large corporation that got hit hard by antitrust. Think a few tens of billions of dollars. Why? A seller was caught giving freebies if they bought their products. That's it. That's all it took.

I know because due to that incident we had to follow online formation every god damn month about antitrust. You don't have to have a "monopoly" to trigger antitrust legislation. The mere mention of "deals" or "cooperation" or "understanding" in the same conversation that involves competitor can be enough evidence to cause huge trouble.