The customer is NOT always right!

But they ARE always the customer! Seeing that it is easier to retain current customers, than win over new ones - it is an essential balancing act to manage your customer orientation. 

Here are three possible scenarios:

1.) Clarify expectations: Unmet expectations are the enemy. This leads to two wrongs - their perception, and yours. To avoid this, make sure you are both on the same page before you start.

2.) When they get it wrong: And inevitably this happens at one point or another. Show them that you are willing to go the extra mile (within reason, and without abuse of you as supplier). This will not only retain the client, but can potetnially win you the next referral. Ask neutral, clarifying questions, with a genuine attitude of wanting to resolve the disconnect.

3.) Retain Integrity: If you are the subject matter expert (whether in sales or services), and your client's adamant request poses a risk to them - then resist respectfully. If you really have their best interest at heart, your humble assertiveness will win far more respect, than what you fear you may loose in the short-term. 

Remember - it is only in algebra, where two negatives multiply to make a positive!