Is There a Ban on Self Preferencing?

ios developers complain that they don't get access to who their customers are. There's probly a lot of room for westeveloperis getting a lot more information on who's buying the raps. And amazon are in a lot of trouble with the commission, because they monitor what happens in the store and then release their own amazon asentials product to compete with it. The last one is that gatekeepers can't rank their own services higher than others.