elfbiter

Piers Anthony - Prostho Plus
(Repost from Livejournal)
Dr. Dillingham is a human dentist who suddenly has to treat a denizen of a flying saucer. After the successful treatment, the grateful proto-Greys abduct him and sell him in outer space. Poor doctor gets acquainted with number of (amusingly) alien species and their various dental problems. Eventually he finds himself in the Galactic University of Dentistry and faces its internal politicking.
( Major drilling work for Dillingham )

Keith Laumer - Retief At Large

Jaime Retief is a secondary level diplomat in the CDT - Corps Diplomatique Terrestrienne - that represents the interest of Earth humans ("terries") in the galaxy. The main political opponent of humans are the Soviet analogue aliens named Groaci, who are just about as devious as you can think of.

( Only competent human diplomat in the galaxy )