PHRASE
（貨物等）來路不明，是老鼠貨，是賊贓
If someone says that something has fallen off the back of a lorry, or that they got something off the back of a lorry, they mean that they bought something that they knew was stolen.
例句
He gets caviare that has fallen off the back of a lorry...
他能弄到來路不明的魚子醬。
Pete once bought the boys a bicycle cheap off the back of a lorry.
皮特有一回給孩子們買了一輛便宜的老鼠貨自行車。