I wrote a post for CMSWire last week that has resonated with a surprising number of readers. In it, I noted that social media has reversed the traditional sales and marketing paradigm. Once upon a time, a transaction was the trigger for building relationships – and the repeat customer was the holy grail.

Today, of course the repeat customer still matters, but the relationship between a business and its customer now begins well before the initial transaction.

This has powerful implications for communities, which are often the place where potential customers are first connecting with organizations, in both a positive and negative way. A positive community/social media experience can drive a customer to transact business, but a positive initial experience coupled with a poor experience during the transaction can actually be a net negative for a brand.

Steve Garfield has recently written a series of posts about his experience with Mercedes, where a quick social media reaction to a frustration he was feeling about a test drive not only led to him being more enthusiastic about the car and the brand, it actually inspired him to invest in a dealership.

But it can work the other way as well. In the market for a new car, I had my mind pretty well made up on what I wanted. It was fairly expensive, but I had done my research, had developed a strong track record with the brand, and went into the dealership ready to buy – title in one pocket, checkbook in another.

One hour later, the transaction was so painful, I left with my title and checkbook intact and wavering on my decision. A day later, I had more or less decided not just to walk away from the dealer, but from the brand as well.

Think about that. I walked in ready to buy – and to spend tens of thousands of dollars. I left rethinking whether I would ever buy from the brand again. Why? Because those conducting the transaction ignored the relationship completely. They were so anxious to get the transaction that they did irrevocable damage to the relationship. What should have been a sure thing turned into to a complete failure.

They failed to recognize a number of things. Among them:

• In the social media era, your customer often doesn’t need you to sell them something, they need you to help them buy what they want.

• The best customers come in very well prepared and well informed – don’t give them a salesperson who knows less than they do.

• If your employees cannot match the enthusiasm the customer has for your product, you have ignored the most powerful asset you have available to you – shared value.

• Increasingly, the only reason the customer goes to a physical store is to confirm that their research matches the physical experience of the product and service and to sort out the details of the transaction.

• If the customer’s needs cannot be met, helping them understand their alternatives is good. Trying to corner them into a transaction is not. By doing the former, you might generate an even larger transaction. By doing the later, you lose what was close to a sure thing.

• Respect – which practically means not making assumptions, asking a lot of questions and understanding the customers constraints – was always a good idea in sales, and now is more important than ever.

And there’s one more thing:

• The higher your customers’ expectations of you, the more damaging it is when you fail to meet them.

That’s not to say you have to bend over backwards for customers with unrealistic expectations. But you need to recognize that failing to meet expectations can be devastating. In the case of my car buying experience, it has been very tempting to rip the brand I once loved on social media and in review sites. I haven’t – but if I see someone mentioning they are considering a purchase, I will tell them my story.

That hidden cost then is that they haven’t just lost one buyer. They’ve also failed to acquire another. That five-figure loss? Now it approaches six figures.

If that customer has become a part of your community, he or she has access to your fans and followers in a way that you have never experienced before. He or she may have already been talking about their excitement entering the transaction. If that excitement turns to disenchantment, they have an audience that will want to know why. The good news is that by having a community, your brand advocates have an avenue to rush to your defense and you have the opportunity to fix the situation. The bad news? Your advocates have allegiance to your brand, but also to the community and if they think the community member is right, you best be prepared to deal with it.

Social media and community allow you to build relationships with your brand and create lifelong advocates before they ever transact business with you. But if you fail them during the transaction, you create a customer who is empowered and dissatisfied – and that’s a dangerous combination.