 Why is Simon so unenthusiastic when the client shows up at the beginning of the story?
He looked over at Betty and said, almost as though reciting, "What I need is a vacation." "Providence," Simon told her whilst fiddling with the aspirin bottle, "will provide." The client fussed himself with Betty's assistance into the seat, bug-eyed Simon, said finally, "You know my name, that's pretty good. When Simon continued to say nothing she ventured, "Time travel is impossible." "Then you'll realize that there are a dozen explanations of the paradoxes of time travel. It's my contention that within a century or so man will have solved the problems of immortality and eternal youth, and it's also my suspicion that he will eventually be able to travel in time. "The usual explanation, Betty, is that they can't afford to allow the space-time continuum track to be altered. Mr. Oyster returned his glasses to their perch, bug-eyed Simon, but then nodded. Simon said, "You want to hire me to find a time traveler and in some manner or other—any manner will do—exhort from him the secret of eternal life and youth, which you figure the future will have discovered. It takes roughly seven and a half hours from Gander to Shannon and I spent that time dreaming up material I could put into my reports to Mr. Oyster.
 He knows he cannot accomplish what Mr. Oyster is asking, and knows he will have to turn him away.
 He knows Mr. Oyster's reputation, and does not want to get involved in his affairs.  He knows he cannot accomplish what Mr. Oyster is asking, and knows he will have to turn him away.  He only takes on easy cases that he knows will pay the bills.  He has too much of a headache to deal with the new client.