According to a lot of business advice books, the key to success is a happy staff. But it seems, as has been pretty widely reported, fast food chain Pret A Manger likes to take this one step further. According to its in-house literature Pret ‘only employs people who are friendly and lively… people who are good-humoured by nature’.

The chain’s chief executive, Clive Schee, said: “The first thing I look at is whether the staff are touching each other. Are they smiling, reacting to each other, happy, engaged? I can almost predict sales on body language alone.”

Pret welcomes workers who high-five colleagues as encouragement and ‘create a sense of fun’ and ‘care about other people’s happiness’. And they have a list of ‘emotional labour rules’, which are behaviours that are desirable for workers – things like touching each other (appropriately, of course), not being moody and not being there just for the money. Working there is about more than just selling coffee and sandwiches, apparently.

All this might seem a bit crazy and a little over the top for a fast food chain. Especially when a lot of their staff are earning little over minimum wage and for them it’s just a part time job to earn a bit of money while studying. It seems a little unfair to ask all this of them – and to be checking up on them with visits from mystery shoppers every week.

But when we spoke to a Pret employee, we were pretty surprised to find out that these rules aren’t viewed as an annoyance or something stupid from management that is generally ignored.

She said: “If the employees don’t enjoy their job, it’s obvious, and it rubs off on the customers. At Pret, we want to give our customers a positive experience, and it helps if we’re positive ourselves – who wants to be served by a grumpy worker?

“I’ve worked at Pret for a number of years and really enjoy it. Our team get on and many of us are great friends outside of work too. Like everyone, we all have days where we don’t feel as great, but I always try and stay positive for the sake of providing a great experience to our customers and upholding Pret standards. Great customer service can really make someone’s day.”

There is an incentive for Pret’s staff to follow their guidelines on ‘Pret Perfect’ behaviour. If they receive a good report on their weekly mystery shopper visits, everyone receives a cash bonus. However, if one member of staff is found to be insufficiently enthusiastic or, dare we suggest, miserable, then everyone misses out.

This might seem a little harsh but maybe Pret is on to something here. The chain has a good record of staff retention. In 2011 they took on 58 apprentices and more than 75% of them were still working with the company six months later, which accord to the financial director Nick Candler is “an extraordinarily high percentage.”

And let’s be honest, who doesn’t love service with a smile? Do you work in the food service industry? Check out our tips on how to be the best waitress possible and how to gain transferable skills from your job.