Off the back of a lorry
The idiom, obviously, is a comparatively modern one (lorries, after all, are quite modern!). Its popularity dates back to World War II, when the selling of illegal goods became quite common. The phrase very simply refers to buying something that was stolen. The term was first used in the USA and Australia, where it popularly becomes ‘fall of the back of a truck’. In 1928 in the records of the Australian House of Representatives it says: ‘We heard, through something that had fallen off the back of a truck onto a reporter’s table.’
In the UK, The Essex Chronicle in 1937 writes of the theft of some chickens, where the accused, ‘prisoner said ‘they fell off the back of a lorry’.’ The Times, in 1968, talks of: ‘The suggestion of the finder, a casual motorist, that the records ‘must have fallen off the back of a lorry’.’
I bought it from an outdoor market for cheap, possibly being sold having fallen off the back of a lorry.
Tony has a clean record, except for that one time he bought a motorcycle fallen off the back of a lorry.
The shop around the corner sells electronics got off the back of a lorry. I would be wary about shopping there.