Tom is sitting in a hotel lobby, facing the reception desk, and observing customers checking into their rooms. He is playing a game with himself where he tries to guess whether each customer is visiting on vacation, or on business. On one occasion, he sees a new customer, in neutral clothes, walk up to the reception desk, and the hotel clerk fetches the customer his room key. There was no communication, verbal or otherwise, between them.
Because of this behaviour, and only this, Tom is almost certain that the man is there on business rather than on vacation, even though he has never met or even seen this man before. Why is Tom so sure of this?
The clerk had never met, seen or spoken to the man before, and was not aware that he would be arriving on that day
As the man is standing at the reception, the clerk also knows which company the man works for, but Tom does not
The man is attending a conference