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There have been a variety of Muppet salesmen in various Henson productions.
Sesame Street
Grover sometimes works as a sales monster.
Telly Monster once worked as a salesman, selling Kermit a head warmer.
The Encyclopedia Salesman
The Muppet Show
A handcuff salesman appeared in a "Bear on Patrol" sketch.
Chopped Liver once worked as a salesman for Spumco in a "Pigs in Space" sketch.