Lobbyists who are viewed as nice, trustworthy, courteous, honest and helpful are more likely to get elected officials to buy in to their point of view.

That was one of the themes that emerged from research I’m conducting for a book about grass-roots rock stars who have not just advocated for their cause, but were so persuasive that they changed the minds of elected officials. I interviewed 20 or so elected or former elected officials who were on the other end of their lobbying efforts, and each one cited behavioral characteristics of the advocates as a reason for their effectiveness.

Toby Moffett, a former Democratic Congressman from Connecticut, still remembers how well union members, one of his core constituencies, treated him when he told them he was on the fence about the first Chrysler bailout. Moffett, who served from 1975 to 1983, told the members he had a strong libertarian streak that was making it difficult to vote for the bailout.

“When they found out I was on the fence, they could have unleashed their forces on me,— Moffett recalled. Instead, they gave him room to ruminate. When it came time to vote, Moffett said, he saw “all these union guys in the gallery, and I remembered how they treated me.— He voted for the bailout.

If the idea seems obvious, consider that the elected officials cited plenty of stories about advocates who weren’t nice.

JoAnn Davidson (R), a retired state legislator who was Speaker of the Ohio House from 1995 to 2000, described how lobbyists from one of the most powerful advocacy groups in Ohio, who should know better, routinely tried to win her vote by “fist pounding— on her desk or making threats and demands.

Davidson said she was well aware of the lobbyists who were friendly year-round and the lobbyists who were friendly until two months before Election Day — and then kept her at arm’s length until after the ballots were counted.

“Being nice doesn’t cost you a cotton pickin’ thing and it helps immensely,— she said.

Former Florida state Rep. Janegale Boyd (R) was voted one of the most pro-business legislators by the Florida Chamber of Commerce, but she balked when representatives of a major professional sports franchise asked her to support a $45 million proposal for a new baseball stadium in 2005.

Boyd said she was turned off by the team representatives who “had an exaggerated sense of their own importance.—

“I think they felt that because of who they were they did not need to sell their issue to me,— she said.

You have got to sell your story — and nice lobbyists also have enough emotional intelligence to know that it isn’t smart to push an elected official to make a decision before he or she is ready.

It is an article of faith in the influence business that you have to be passionate about your cause to succeed. But the elected officials said lobbyists who spoke passionately about their issues sometimes shot themselves in the foot by talking too much and pushing too hard.

I call them “yaktivists.— Retired Rep. Jim Ross Lightfoot (R-Iowa) was one of many elected officials who said he was more likely to listen to lobbyists who were polite and laid-back.

That counterintuitive finding illustrates an idea I’ve been pushing for the 11 years I’ve been training grass-roots influencers how to not just advocate, but to persuade: Underdogs can get a leg up on the competition if they don’t mindlessly follow the crowd. This idea was underscored in a recent New Yorker piece by Malcolm Gladwell, who also concludes that underdogs prevail when they use unconventional tactics and substitute effort for ability.

I wanted to find out if the pros are nice — the professional lobbyists. Aren’t they ruthless, win-at-all-costs negotiators? The American League of Lobbyists and I asked its nearly 900 members to name the nicest lobbyists they knew and explain what behaviors made them nice. Interestingly, four of the top six vote-getters also have appeared on recently published lists of the most effective lobbyists.

Brian Pallasch of the American Society of Civil Engineers was among 13 of the most effective lobbyists on a list compiled by CEO Update. Paul Miller of Miller/Wenhold Capitol Strategies was named as a top lobbyist by Association Trends magazine.

Pallasch says it’s all about respect — respecting the perspective of your influence target, his time and how he prefers to be communicated with. Rick Shelby, a lobbyist for the American Gas Association who has also been cited as a nice — and effective — advocate, said lobbyists who are polite ultimately get more consideration.

“If you are mean, you better hope your argument is so meritorious that it’s unassailable,— he said. “Nice people are given the benefit of the doubt, because many decisions made here are highly subjective.—

Amy Showalter is president of the Showalter Group, a Cincinnati-based firm that advises trade associations, Fortune 500 companies and nonprofit organizations on how to increase their grass-roots and political action committee effectiveness.