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trade down
Sell something and replace it with something cheaper
trade up
Buy larger or more expensive items
Leave your wife or husband and marry someone better looking, richer, etc
trade off
Bargain, make a deal or compromise
Accept something you don't really want to get something you do want
trade in
Exchange something old as part of the price of something new
Leave your wife or husband to marry someone younger
trade upon
Exploit, use to your advantage
trade on
Exploit, use something to your advantage