"When you say something 'fell off the back of a lorry', what you mean is that it was received in suspicious circumstances. It was probably stolen:
The police have been looking for a local man who doesn't mind selling mobile phones that fell off the back of a lorry."
For listening comprehension practice, visit the BBC site 'Learning English' (the English We Speak, 29 April 2014), which is where I have taken today's idiom definition and example from.
Going by the book
Hace 5 semanas