'Tell you who I had in the back of this cab - a Thailand tourism promoter. Lovely man.'

Positive word-of-mouth advertising is the Holy Grail for most marketers - it's free and it carries a ring of legitimacy that can't be bought. Which helps explain why companies have started recruiting taxi drivers as "brand ambassadors" - essentially paying them to be walking (or driving, as the case may be), talking adverts. Taxi drivers have already been signed up and treated to free holidays, according to the Evening Standard - for example, one cabbie was treated to five days in Bangkok courtesy of the tourism authority of Thailand and has wasted no time in evangelising it as a holiday destination to his fares. So it's not enough that you have to endure a cabbie droning on about the ills of the modern world, now you have to wonder whether they are trying to sell you something as well.