Managing expectation of the team, clients and boss

How many times you have faced problems because you could not manage the expectations of the team members, boss or the client. It is one of the biggest source of conflicts between the (inter or intra) teams.
I give you an example how the expectations of the client can go up and if we don’t manage them well they can create problems. One of friend was working on the change management project on a client site. In the change management project, privacy of the employees on the client site is very important because if this is not ensured then no one will reveal any information about the organization. During the project, they were interviewing the different teams on the client site. After the interview of team A, the boss of the company asked how was the team, they replied it went very well, team was very cooperative and helpful etc etc. Next the consultants interviewed team B and again the boss came in the evening and asked about the team B. Now the consultant said that they had a contract that they will not reveal any private information about any employee. But the consultant had already done the damage to team B. Telling good things about team A and not telling anything about team B was an indication that there was some problem with team B.
It is better to manage expectation at the beginning rather than waiting till late. Expectation of the clients or the boss or the team always keep increasing so don’t let them become dragon and get trapped in the problem.