Papers suggests the mechanism for the cost reduction by the belief control. It suggested the mechanism that could be usefull to reduve costs and satisfy all these requirements just by belief control, though belief control is a hard problem itself. Authors consider market of manufactures with utlity function as in Cournout competion with quadratic costs. Authors make suggestions on beliefs and knowledge of agents weaker in terms of common knowledge and found domains of parameters where utility increases and where it decreases when we change the beliefs of players. These results provide important insights into the properties of information control for the chosen games. The stability restrictions are restrictions on the utility functions by obervability and exceeding minimal value.