N-UNCOUNT [oft in NOUN] 以旧换新 If you give an old item in part exchange for something you are buying, the seller accepts the old item as part of the payment, so you do not have to give them as much money. 以旧换新 [British]
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Electrical retailers will often take away old appliances if you buy a new one, sometimes in part-exchange.
买新电器时，电器经销商往往会拿走旧电器，有时会以旧换新。
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...part-exchange deals.
以旧换新