There is nothing mysterious about persuasion, although plenty of people would like you to think there is. When Professor Robert Cialdini set out to understand why some requests succeed and others fail, he did something unusual for an academic: he went undercover, training inside sales teams, fundraising operations and advertising agencies to watch persuasion happen in the wild. What he found was that beneath all the patter and technique, the same small set of psychological principles was doing the work every time. He described them in his book Influence: The Psychology of Persuasion, which remains the single best thing you can read on the subject — and if these summaries whet your appetite, you should read it in full.
What follows is each principle in turn, with examples of how it appears when people buy and sell, and how a business like yours can use it well.
1. Reciprocity
Reciprocity is a social convention found in every society on Earth: when someone gives us something, we feel we must repay it in kind. The obligation arrives whether we asked for the gift or not, and it does not even depend on liking the person who gave it. An uninvited first favour still creates the debt.
The effect is remarkably strong. In one much-cited test, a charity’s direct mailing produced roughly twice the donations when a small free gift — a pen — was included in the envelope. The pen cost pennies; the feeling of obligation it created was worth far more.
Reciprocity even works when a request is refused. Turning someone down leaves us with a quiet urge to make it up to them, which is why a refusal is not the end of a sales conversation. If a client says no to the main proposal, asking for something smaller — a referral, an introduction, a second meeting later in the year — often succeeds precisely because it lets them rebalance the exchange.
For your business, the lesson is to give something of real value first. A useful guide, a free audit that surfaces something they did not know, a consultation that leaves them better off whether or not they hire you — each of these creates the pull of reciprocity honestly, because the value you gave was real.
2. Commitment and consistency
Once we have taken a position, we come under two kinds of pressure to stay consistent with it: internal pressure, because we like to feel our decisions make sense, and social pressure, because we want others to see us as reliable. In a sales context this means that once a client has expressed interest in a product, or agreed that a particular benefit matters to them, they are unlikely to reverse themselves. Stranger still, once the commitment is made we go looking for new reasons to support it — and the commitment survives even if the original incentive that produced it is taken away.
That last quirk is the engine of a notorious technique called the low-ball, where a salesperson offers an attractive price, waits while the customer sells the product to themselves, and then withdraws the price knowing the commitment will usually survive. Do not use it. It closes one sale and poisons every future one, because the customer eventually understands what was done to them.
The honest application is to design your customer’s journey as a staircase of small, easy commitments rather than one giant leap. Someone who downloads your checklist, then replies to a question, then books a short call has been becoming your customer at every step — and each yes makes the next one feel like the natural continuation of a decision they have already made.
3. Social proof
One of the most fundamental ways people decide what to do is to look at what similar people have done. The proof of what is correct is not found in the physical world but in the social one: if a lot of people like me are doing it, it must be the right thing to do. The more people who appear to hold an idea, the more correct that idea feels — quite independently of whether it is.
This is why testimonials from satisfied clients, reviews, and referrals carry a credibility that no amount of self-description can buy. A business saying “we are excellent” is making a claim; a customer saying it is providing evidence.
There is one rule that matters more than all the tactics, though: social proof must be real. Invented reviews and borrowed praise are not just wrong, they are fragile — the moment a customer senses the proof is manufactured, everything else on the page becomes suspect too. Show only what is true, make it easy to check, and the principle works twice as hard for you. (It is why you will find no testimonials on this site yet: we would rather show you none than show you anything invented, and the ones we publish in time will be real.)
4. Liking
People want to say yes to people they like — a fact so reliable that whole industries were built on it. Direct selling to friends and relatives works because the liking arrived before the salesperson did, and the old “endless chain” method formalised it: find one person who likes the product, ask them for the names of friends, and approach those friends carrying the warmth of the referral with you.
Research fills in what makes us like people in the first place: similarity to ourselves in background, dress and manner; genuine compliments; familiarity; and, less comfortably, physical attractiveness, which we unconsciously read as evidence of other good qualities. This is why building honest rapport with a customer is not small talk — it is the foundation the whole conversation stands on.
For a business selling online, where nobody meets anybody, liking translates into voice and visibility. Write the way your customers speak rather than in corporate language. Show the real people behind the business. Admit the odd imperfection. A recognisable human being is likeable in a way a faceless company can never be.
5. Authority
People are more easily influenced by those they perceive as legitimate authorities, and the response is mostly sensible: real authorities usually earned their position through greater knowledge, skill or experience. It is why the doctor’s advice and the lawyer’s letter carry weight before a word is read, and why status signals — the title, the track record, the confident command of detail — change how a message lands.
The useful subtlety for your business is that demonstrated authority beats claimed authority every time. Calling yourself a leading provider persuades nobody; a page that explains precisely how the work is done, in language that shows you have done it many times, persuades quietly and permanently. Publish what you know. Teaching is the most credible advertisement there is — it is, you may notice, the principle this entire section of the site is built on.
6. Scarcity
The scarcer something is, the more valuable it appears — and the prospect of losing an opportunity moves people more powerfully than the prospect of gaining one. Every “last one in the shop” and “offer ends Friday” is pulling this lever.
Which is exactly why scarcity is the most abused principle on this list. Two pressure tactics in particular are so common they have names. The limited-number technique has the salesperson claim the product is nearly sold out when it is not. The deadline tactic invents a date after which the price rises or the product vanishes. Both are effective in the moment, and both are ways of losing a client in the long term, because manufactured urgency is eventually recognised for what it is.
Our rule — and the one we would urge on you — is that scarcity may only ever describe reality. A diary that is truly limited, a price that really does rise next quarter, a genuine cost of waiting: state these plainly and without apology, because they are facts your customer deserves to know. The moment scarcity departs from the truth, it stops being persuasion and becomes a trick.
7. The contrast principle
Beyond the six principles sits one more, which frames how all the others land: nothing is judged on its own. By placing two things side by side you create a scale with one at each end, and each is measured against the other rather than against the world. An expensive item makes the next item look cheap; a £90 jumper feels like nothing when it follows an £800 suit, which is why good tailors sell the suit first. Estate agents have been known to show a poor property before a good one, because the good one shines brighter by contrast.
Once you see the contrast principle you will find it everywhere — and you can put it to honest work in how you sequence your own prices, proposals and options. The order in which choices are presented changes how each is perceived, so a well-built pricing page or proposal is not just written; it is arranged.
Where the line is
Every principle here has an honest version and a manipulative one, and there is a single test that separates them: would it still work if the customer could see exactly what you were doing? Real reciprocity survives daylight; the low-ball does not. True scarcity survives daylight; the invented deadline does not. Persuasion built on true things compounds, because every satisfied customer makes the next sale easier. Persuasion built on tricks borrows against your future reputation at ruinous interest — and in a business you intend to run for years, that is the worst deal on this page.
Would it still work if the customer could see exactly what you were doing?
The research behind thisRobert B. Cialdini, Influence: The Psychology of Persuasion (1984, revised 2021). Source →
Robert B. Cialdini is Regents’ Professor Emeritus of Psychology and Marketing at Arizona State University. If this subject matters to your business, read the book — it repays every hour.
These principles are the working method behind our copywriting. More about copywriting →