There's a park I walk through on the way home each day. It used to be a very pretty park with vast areas of green freshly clipped grass, commemorative benches with gleaming plaques, pristine toilets that won countless awards, trees that have been there for decades and freshly painted playground equipment for the kids to climb over.

About a year ago I happened to notice that one of the windows of the toilets had been smashed, I could have been wrong, but it looked like someone had thrown a stone through it. I tutted to myself and continued on my way. The next day as I was walking, I noticed that someone had added to the broken window with another and someone else had scrawled their name next to it in giant, sprayed on letters.

Over the year, things have got worse. The green grass has yellowed and is littered with rubbish, the benches have become worn and broken in places and the playground is more rust than paint and seems held together by the marker pen graffiti.

A sad tale of urban decay you may be thinking, but what the heck has it got to do with sales?

The thing that tripped off this series of events was the broken window. I would argue that had that broken window been fixed the day after it's breaking then the person who broke the second window and left graffiti would not have done so. Consequently the park would not have become an area where it was ‘ok' to treat with disrespect and it would not have fallen into steady decline.

Again I hear you thinking, I get it, but what the heck has that got to do with sales?

Let's say you have a team and in the majority they are pretty successful with sales. They are all doing ok and you can see that their skills are developing progressively. However, there is one member of the team that is not on board with the concept. They are disruptive, they complain, they challenge every product by comparing it negatively against competitors and they do their utmost to undermine the process at every opportunity.

Many managers will ignore this person in the hope that they will get so fed up that they move on to another part of the business or even to the competitors they so admire. They'll invest little time in them and ignore their development. This is a mistake. The person we have described is your ‘broken window' and all the time they are left ‘un-mended' they will encourage the same negative behaviour in others, until your business looks as tired and worn as the park I go through every night.

Other people will start to model the behaviours displayed by the broken window and you will notice a steady decline in sales development, after all, 'if they can get away with it, maybe I can too'. It is far easier to change the methods of one than it is to alter the habits of one hundred.

I would even go further than this and say that they are the catalyst and, if turned around, they will move your culture of sales on to the next level. When negative obstructers, who generally court a lot of influence, become flag wavers for the business, you have found a method of ensuring that things happen even when the boss isn't looking.

Like mending a broken window, it's not fun and nobody wants to spend the time, money and effort on it, but it's a lot better than having to re-develop the whole damn park.