PHRASE
（货物等）来路不明，是老鼠货，是贼赃
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...
他能弄到来路不明的鱼子酱。
Pete once bought the boys a bicycle cheap off the back of a lorry.
皮特有一回给孩子们买了一辆便宜的老鼠货自行车。