Ever since Robert Cialdini wrote Influence it's been the go-to book for business owners and marketers wanting to understand the psychology of their customers and the little tweaks they can make to influence them to buy more.

And it's been taught in thousands of courses on marketing.

One of the cornerstones of Influence is the concept of Reciprocity: that if you do something good for someone, they'll do something good for you in return.

There are lots of prominent examples of reciprocity: the waiter giving an extra mint and getting a bigger tip for example.

We've applied it to online marketing too: we give away free stuff in the hope it'll encourage people to buy from us.

But new research published in the Annual Review of Economics last year (in an article entitled Rethinking Reciprocity) has highlighted that the concept might not work quite the way we originally thought.

In particular, it's looking like reciprocity may be a lot less to do with an innate human desire to return favours and more to do with the social pressure to be seen to return favours.

That doesn't make much difference to our waiter: he or she still gets a bigger tip by leaving that extra mint because everyone at the table is a witness to the act and there's social pressure on the tipper.

But for those of us who market online, it's difficult to harness social pressure when our customers are sitting alone in front of a computer screen and no one knows what they're doing.

Now I'm not saying we should abandon all our ideas of reciprocity just based on a small scale laboratory experiment.

But it's worth thinking about.

In particular, if you want reciprocity to work for you online you probably need to make a personal connection. Let the “recipree” (if that's a word) see a photo of you or watch you on video. Connect with them on social media or send a personal email.

Of of course, you could follow my preferred strategy: do good things for people because it's the right thing to do, not because you expect to get a reward some time in the future :)