Fabric salesman in city going west (5)
I believe the answer is:
crepe
'fabric' is the definition.
(crepe is a kind of fabric)
'salesman in city going west' is the wordplay.
'salesman' becomes 'rep' (I've seen this before).
'in' means one lot of letters goes inside another.
'city' becomes 'ec' (the City of London postcode).
'going west' says the letters should be written in reverse.
'ec' backwards is 'ce'.
'rep' put inside 'ce' is 'CREPE'.
(Other definitions for crepe that I've seen before include "Material - French pancake" , "French dish" , "Light wrinkled fabric" , "sole?" , "Pancake - type of paper" .)