Artist group - the first to buy and sell clothing business (3,5)
I believe the answer is:
rag trade
'clothing business' is the definition.
(I've seen this before)
'artist group the first to buy and sell' is the wordplay.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'the first' indicates taking the first letters.
'to buy and sell' becomes 'trade' (I've seen this before).
The initial letter of 'group' is 'g'.
'ra'+'g'+'trade'='RAG TRADE'
(Other definitions for rag trade that I've seen before include "National winner" , "The couture business" , "Commonly, the clothing business" , "The fashion business" , "Clothing business (colloq.)" .)