One-for-one trade (4)
I believe the answer is:
swap
'one-for-one trade' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for swap that I've seen before include "Exchange, barter" , "Fifty-fifty odds" , "Substitute' feet backwards" , "Exchange; hands back" , "Wasp (anag)" .)