The short story was in a collection of short stories. An Earthman takes an exam in an interplanetary contest on ethics and wins. He becomes a part of an interplanetary government. He lacks the ability to read minds as most can. He detects a lie from one other new planet without telepathic ability. It is probably pre 1990. Does anyone know the story name, author, or collection?
This would be "Ethical Quotient" by John T. Phillifent which first appeared in the October 1962 Analog. It was reprinted in Analog 2 and in the Analog Anthology.
Its a perfect match for your description. The human is picked as an "ethical absolute" by a sophisticated testing system, but the aliens who administer it are shocked that -- alone among intelligent races -- humans are not telepathic and are completely invisible telepathically. There's a crime aboard the ship, and the human works out the answer, and it turns out that all humans who had met aliens had been wearing telepathic shields which had been (inadvertently) developed as a tool to prevent human presence from affecting the touchy star drive.
So humans are telepathic, and this particular human is a genuine ethical absolute and he'll go on to be part of the galactic government.
(It's a nice story.)