Artist group - the first to buy and sell clothing business (3,5)
I believe the answer is:
Here is my best explanation:
'clothing business' is the definition.
(I've seen this before)
'artist group the first to buy and sell' is the subsidiary indication.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'the first' suggests taking the first letters.
'to buy and sell' becomes 'trade' (I've seen this before).
The first letter of 'group' is 'g'.
(Other definitions for rag trade that I've seen before include "National winner", "newsagent's business?", "Slang for the garment industry", "Garment industry", "dressmaking competition", "Fashion industry (informal)", "Clothing industry", "The couture business", "The fashion business" and "Clothing business (informal)".)