I'm not sure about tailored fit for plain clothes (5)
I believe the answer is:
mufti
'plain clothes' is the definition.
(I've seen this in another clue)
'i'm not sure about tailored fit' is the wordplay.
'i'm not sure' becomes 'um' (expression of hesitation).
'about' shows that the letters should be reversed in order.
'tailored' indicates an anagram (the letters are customised ).
'um' back-to-front is 'mu'.
'fit' anagrammed gives 'fti'.
'mu'+'fti'='MUFTI'
'for' acts as a link.
(Other definitions for mufti that I've seen before include "Ordinary clothes" , "Plain clothes - Muslim legal expert" , "Civilian dress, in army terms" , "For soldiers, civilian dress" , "Civilian clothes worn by service personnel" .)