Commercial muck right for fan (7)
I believe the answer is:
admirer
'for fan' is the definition.
(an admirer is a fan of something)
'commercial muck right' is the wordplay.
'commercial' becomes 'ad' (abbreviation for advertisement).
'muck' becomes 'mire' (mire can mean muck or dirt).
'right' becomes 'r' (common abbreviation).
'ad'+'mire'+'r'='ADMIRER'
(Other definitions for admirer that I've seen before include "A young lady's beau - he thinks she's great" , "Married to one who cherishes" , "Married (anag) -- lover" , "One who regards (someone) with respect" , "One who cherishes, like boy friend" .)