trouble shooter vs service man

trouble shooter and service man both are nouns.

Word	Noun	Adjective	Verb	Adverb
trouble shooter	Yes	No	No	No
service man	Yes	No	No	No

As nouns, service man is a hypernym of trouble shooter; that is, service man is a word with a broader meaning than trouble shooter:

trouble shooter: a worker whose job is to locate and fix sources of trouble (especially in mechanical devices)
service man: a skilled worker whose job is to repair things

Other hypernyms of trouble shooter include maintenance man, repairman.

trouble shooter (noun)	service man (noun)
a worker whose job is to locate and fix sources of trouble (especially in mechanical devices)	a skilled worker whose job is to repair things