Joiner turned up with three experts (7)
I believe the answer is:
maestri
'experts' is the definition.
(I've seen this before)
'joiner turned up with three' is the wordplay.
'joiner' becomes 'seam' (area which joins two bits of fabric).
'turned up' shows that the letters should be reversed in order.
'with' is a charade indicator (letters next to each other).
'three' becomes 'tri' (prefix meaning 'three').
'seam' reversed gives 'maes'.
'maes'+'tri'='MAESTRI'
(Other definitions for maestri that I've seen before include "Experts" , "leading musicians" , "Top musicians" , "Distinguished conductors" , "masters" .)