If people don't believe the message, then not only is there no possibility of a positive response, but the chances of a negative one increase dramatically. No-one likes being taken for a fool.
My unscrupulous friends in PR - who tend to be the more amusing if not always the most prosperous - have it as an article of faith that they always tell the truth, at least in the beginning. Only when trust has been properly established can they hope to get away with stretching things a bit. And even then most reckon it is just not worth over-egging it.
Today we live in an age of unprecedented sophistication in media. So why do journalists receive - and public relations professionals send out - so many releases that lack credibility, and that therefore risk doing reputational damage to the client?
There was a case in point last week with the announced merger of two firms of consulting actuaries and benefits consultants. I will delete their names but this merger was announced in the following terms: 'We will have deeper resources to serve you by bringing together the extensive expertise of our organisations. We will deliver exceptional quality and seamless service ... We share an unwavering commitment to our clients and friends, and our priority during this time is our service to you.'
Only an idiot is likely to take this at face value. Does anyone really think it is better to have a choice of one giant monopolistic firm rather than two that had been in competition? Does anyone know of a professional firm merger that was not scarred by infighting? Do these things ever happen without an increase in fees, and feebly embarrassing attempts at cross-selling?
What the press release should have said is they want to get bigger so they can pay themselves more, and they expect the clients to grumble but put up with it.
Not very tactful I admit, but a lot closer to the truth.
Anthony Hilton is City commentator on London's Evening Standard