Minor source of faultless service around the shopping centre (7)
I believe the answer is:
smaller
'minor' is the definition.
(thesaurus)
'source of faultless service around the shopping centre' is the wordplay.
'source of faultless service' becomes 'ser' (I can't justify this - if you can you should believe this answer much more).
'around' indicates putting letters inside.
'the shopping centre' becomes 'mall' (a mall is a large shopping complex).
'ser' enclosing 'mall' is 'SMALLER'.
Can you help me to learn more?
(Other definitions for smaller that I've seen before include "Not as big as" , "Sell ram (anag.)" , "Less extensive" , "More diminutive" .)