Off the back of a lorry

Buying something really good but super cheap? This expression will make you think twice.

Li was offered a brand new computer for a very low price. 
But Finn advises her not to buy it. Listen to the programme to find out why.

http://httpws.bbc.co.uk.edgesuite.net/mp3/learningenglish/2014/04/bbc_tews_off_the_back_of_a_lorry_audio_140429_tews_173_back_of_lorry_audio_au_bb.mp3