A good niece's moving bureaus (8)
I believe the answer is:
agencies
'bureaus' is the definition.
('agency' can be a synonym of 'bureau')
'a good niece's moving' is the wordplay.
'good' becomes 'g' (abbreviation).
'moving' is an anagram indicator (letters are moved around).
'nieces' is an anagram of 'encies'.
'a'+'g'+'encies'='AGENCIES'
(Other definitions for agencies that I've seen before include "Businesses providing specific services" , "Businesses that serves other businesses" , "Businesses that serve others" , "(Travel) offices" , "Service organisations" .)