The best way to persuade someone to do as you wish is to speak moderately quickly, pause frequently and not be too animated, US researchers suggest.
The study analysed just under 1,400 calls trying to persuade people to take part in phone surveys.
Those who spoke very fast, did not pause or were too animated were least successful.
A UK language expert said it showed "it's not about what you say, but how you say it".
The University of Michigan Institute of Social Research study used recordings of introductory calls made by 100 male and female telephone interviewers at the institute.
They looked at the interviewers' speech rates, fluency, and pitch, and then at how successful they were in convincing people to participate in the survey.
Those who spoke at a rate of around 3.5 words per second (moderately fast) were much more successful at convincing people to take part than those who spoke very fast or very slowly.
The researchers, led by Jose Benki, an expert in the psychology of language, said people who speak too quickly are often seen as "out to pull the wool over our eyes", while those who talk very slow are seen as "not too bright or overly pedantic".
The study, funded by the US National Science Foundation and presented to the American Association for Public Opinion Research, also found people thought too much variation in pitch "sounds artificial" and "like people are trying too hard".
Finally, the team found interviewers who paused frequently - around four or five times a minute - were more successful than those who were fluent.
The team suggested the second group sounded "too scripted".
Dr Rachael-Anne Knight, senior lecturer in phonetics at London's City University, said prosody - the rhythm, stress, and intonation of speech - was key to how what people say is received.
"These features can give us a great deal of information, including how the speaker is feeling at the time and how they feel towards us, the listener.
"For example, we have all experienced situations where someone's words could have been taken a number of different ways, but their tone has offended us, hence when people remark 'it's not what he said, it's the way that he said it'.
"Speakers aren't always aware of the different ways in which their prosody can affect their message, so this research is useful in that it identifies some practical ways in which people trying to get others to participate in telephone surveys might improve their success rates.
"It might also have applications to the service industries, and potentially to all kinds of real-life situations".