It is a rare thing to find a customer who will not slip in a "test" question, just so the viewer can do a "dog and pony show" without knowing it, and prove him/herself to them. This is not only rude, but it is also useless.
The customer must be educated to the fact that a good or bad performance on one question does not mean that an equivalent quality of result will be obtained on another question. "The test" only proves how well the viewer can do on THAT question.
An additional problem is that if you "pass the test", the person will usually then try to see if you can pass another, then another, then another. This leads to a situation called"The Juggler's Effect". If you fail even one of the tests, then no matter how many times you pass it, you are seen as a fraud.