✔ 最佳答案
trade in
係指你以折扣價由經銷商買入一件貨品 (取得折扣的因為係, 你要將舊機同時讓出)
If you trade in something such as your old car or TV set, you give it to a dealer when you buy a new one so that you get a reduction on the price.
trade out
相信意思係跟前者相反, 或者講緊以dealer 嘅身份將一件貨品, 跟上述情況一樣, 以折扣價賣出。
參考: Collins Cobuild English Language Dictationary