Trade involving coins (6)
I believe the answer is:
change
This clue is a double definition.
'trade' is the first definition.
(I know that trade is a more specific form of the action change)
'coins' is the second definition.
(change can mean coins)
'involving' acts as a link.
(Other definitions for change that I've seen before include "Loose money in pocket" , "Word for small coins in pocket" , "Best not to do it in 12" , "Alteration" , "Alter, modify" .)