In my recent BusinessWeek.com column, I emphasize that businesses need to be cautious about making promises in their ads. Over the last fifty years, consumers have grown more skeptical and skilled at spotting messages—mainly because they’ve been let down too often. When you make a claim, you invite people to question it.

Enter Avis, with its “Dear Avis” campaign sporting the company’s iconic “We Try Harder” tagline andAvis poster 1Avis poster 2Avis poster 3 embellished with the statement, “At Avis, we’re in the business of treating people like people.” There’s no reason to doubt the veracity of the real-life stories told through the campaign, but every time I read one I worry that Avis is setting itself up for failure. 

Now I don’t know if Avis is any better or worse than other rental car companies. In my experience, they all let customers down too often. Perhaps the people of Avis really do try harder, but it seems somewhat like a hospital claiming that its nurses care more than those at the hospital down the street, or a CEO boasting that his company’s point of differentiation is service, or its people, or some other untenable claim. The problem with such statements is that while they can’t be proven, they most certainly can be disproven in individual customer interactions. And that’s where the unraveling begins, now turbocharged in the age of social media. 

“We try harder” was a breakthrough perfectly suited for its time when it was launched in 1963. And the fact that Avis still claims that the slogan “was – and is – a business philosophy that every Avis employee holds true” is a nice sentiment. The problem is that the world has changed, and Avis promising (for example) to wait for every renter whose flight is late is setting extremely high expectations. Perhaps that’s good, goes the thinking in the executive suite. But I’d hate to be the poor employee who catches the ire of a furious customer when the promise goes unkept through no fault of his own. 

The images above might work well as posters in an employee break room. In its advertising, however, Avis should focus on endearing consumers to its brand–not daring them to call its bluff.