It's not just  salespeople trying to close the deal who rely on persuasion skills. Convincing people to say yes in a subtle manner is essential for marketers trying to influence buying decisions and managers trying to affect the actions of their teams.

Persuasion may seem like an art form and, indeed, some people are naturally more persuasive than others. But with a little help from Robert Cialdini's book, Influence: The Psychology of Persuasioneveryone can tap into good, old-fashioned psychology to hone their own influencing skills. Here are three factors that encourage people to say yes.

1. Reciprocity

As humans, Cialdini tells us, we feel obligated to return favors. Importantly, this is the case even if the favor was unsolicited. This is why companies looking to make sales send out promotional items like pens, and why free trials drive paying subscribers. It isn't just material items that work here, either. Giving advice, help, or content is another way to influence someone's cooperation or purchase.

By giving a little, you can get a lot in return.

2. Commitment and Consistency

Cialdini notes that humans consider consistency a positive trait. We don't like to be seen as inconsistent. So if we say we believe in something, verbally or in writing, our actions typically follow suit.

Cialdini cites the example of toy stores manipulating this technique over the holiday season.

Parents commit to buying their children the latest must-have for Christmas, but the stores run out! The doting parents don't want to let their children down and instead buy other toys. A fresh shipment arrives in January, and, having already committed to getting their hands on whatever gadget or gizmo it is, they buy it anyway, on top of what they already purchased the month before.

This can be used to get a foot in the door, as was demonstrated in a 1966 study called "Compliance Without Pressure." The study proved that seeking a small and simple commitment from someone eventually results in their buy-in or commitment to a much bigger statement or action later.

3. Social Proof

Long before the age of online reviews and social media, humans looked to their peers and those around them to guide their decisions. As humans, our decisions are influenced by what others think.

Cialdini discusses the use of canned laughter to encourage sitcom audiences to laugh. As cheesy and fake sounding as it might be, studies have proven that canned laughter encourages an audience to laugh more and for longer, even at poor jokes.

A separate study compared two messages presented to hotel guests to encourage them to reuse their towels. The first simply presented a standard environmental message telling the guest about the positive impact of reusing towels, while the second message told them what percentage of other guests had reused their towels. The latter message, which relied on social proof, resulted in a significantly larger reuse rate.

This principle can influence buying decisions, too. It's why large e-commerce retailers often employ features like, "What other people bought." It's why testimonials are effective in influencing purchasing, and why employees will look to their peers to help them decide whether something they are doing is the right thing to do.

Persuasion Made Simple

It takes a little time to perfect persuasion. But by giving a little, playing to people's already expressed beliefs, and putting social proof to great use, you're on your way to influencing people to say yes.