In the episode The Case of the Bogus Books
two different guitars were used by Peter Norland.
From time index 03:05, this guitar is a round hole guitar. The shape of
the head stock makes this guitar look like it might be made by C.F. Martin.
This is from time index 49:35.
This guitar is an f-hole or arch top guitar.
The head stock of the f-hole or arch top guitar
shows it was made by Kay Musical Instruments.