Job exchanges? (6)

I believe the answer is:
trades
'job exchanges?' is the definition.
'trades' can be an answer for 'exchanges?' (trade is a kind of exchange). I'm not sure about the 'job' bit.
'job exchanges?' is the wordplay.
'job' becomes 'trade' (I've seen this before).
'exchanges?' becomes 's' (I can't justify this - if you can you should believe this answer much more).
'trade'+'s'='TRADES'
Can you help me to learn more?
(Other definitions for trades that I've seen before include "Buys and sells shares" , "Swaps - winds" , "Exchanges, buys or sells" , "Occupations" , "Barters" .)
