Flawless Irish salesperson has fit eating fish (14)
I believe the answer is:
irreproachable
'flawless' is the definition.
(thesaurus)
'irish salesperson has fit eating fish' is the wordplay.
I cannot quite understand how this works, but
'irish' could be 'ir' (abbreviation) and 'ir' is present in the answer.
'salesperson' could be 'rep' (sales rep) and 'rep' is found within the answer.
'fit' could be 'able' (similar in meaning) and 'able' is present in the answer.
'fish' could be 'roach' (roach is a kind of fish) and 'roach' is found in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Another definition for irreproachable that I've seen is " Beyond criticism".)