Imagine a situation where several people are sent to an interview and only one has to pass. His knowledge is enough for the project. However, the customer asked for the several candidates so he can choose the best one. And the other people from your company are already engaged in other projects and should not get the job.
The question is: How to show that the other candidates are worse and at the same time not make them look stupid?
I've got the point but I need to clarify the primary idea. I wanted to know how another candidate [that should not pass the interview] has to behave at it?
I've left the modified question [1st one] because several answers correspond to it.