WordNet (r) 3.0 (2006):

trade in
    v 1: turn in as payment or part payment for a purchase; "trade
         in an old car for a new one" [syn: trade, trade in]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "trade in":
   bargain, barter, be in, blind bargain, buy and sell, carry, change,
   deal, deal in, dicker, do business, exchange, give in exchange,
   handle, hard bargain, horse trade, horse-trade, interchange, job,
   market, merchandise, retail, sell, swap, swap horses, switch,
   take in exchange, trade, trade off, trade sight unseen, traffic,
   traffic in, truck, wholesale