Considering the intangible character of services and intellectual services, defining the price of a mission has proven relatively delicate. In an extremely competitive environment, a morose economy and increasingly demanding clients, well informed, professional, even setting up, for the bigger groups, “Buyer” directions specialized in the purchase of council and intellectual services, without forgetting the famous success fee, the concept of "price" becoming increasingly essential and in the heart of the strategy even for professional services firms or agencies.