When the workday comes to an end, happy hour or a quick drink at the bar has become a standard way of letting off some steam, decompressing, or catching up with colleagues.

Usually, the last thing on people's mind is business. But if you're looking to develop customer relationships, you may want to take notice next time you grab a seat at the bar.  Why? Because a bartender can tell you an awful lot about how to make customers happy - or extremely frustrated - within seconds.

From the local pub to the trendy speakeasy, all bartenders aren't made equal. It isn't the apron, unique mustache, sleeve tattoos, or large trove of bitters that make you special. Great bartenders fundamentally understand something that the others don't: It's important to mix a good drink, but relationships are the heart of the business.

To learn more about building these relationships, I spent some time with expert bartender Ben Hanten, owner of Ben's and The Copper Room, in Yankton, South Dakota. Here's his top-three list of how great bartenders build customer relationships to drive sales - and how you can too.

1. Acknowledge customers right away, especially when you're busy

Great bartenders do something extremely well that many marketers take for granted. They acknowledge their customers right away.

Think about walking up to crowded bar to order a drink. When you get there, the bartender is likely busy serving other customers.  To make matters worse, maybe they ignore you or fail to make eye contact. You start to feel a little anxious and frustrated, wondering if/when you'll be served. 

"People ultimately want to be acknowledged and recognized," said Hanten. "A good bartender knows that people immediately are at ease if they're just greeted. If you're too busy to wait on them, simply smiling, nodding, or saying, 'Hello, I'll be with you in just a few minutes,' can change the whole future relationship and transaction."

By acknowledging their patrons, great bartenders can allay any concerns customers may have. They know they'll be taken care of. They'd rather wait five minutes to get served after being acknowledged than potentially be ignored at another bar.

2. Anticipate your customers' needs

Great bartenders anticipate.  Bad ones make assumptions. This could be as simple as refilling a customer's water glass before it's empty or asking if they'd like another beverage.

"That inner voice of a customer can be troublesome," Hanten said.  "When a [customer's] glass is empty, they start thinking about where else they should be, what they have to do tomorrow, etc. If, however, we can stay just ahead of the glass going empty, we prevent all that anxiety. And it shows the customers that they're still being acknowledged and cared for."

"A bartender shouldn't ask, 'How are you guys doing?,'" Hanten said, "when the question really is, 'Do you want another whiskey?'"

When you ask customers how they're doing, they'll almost always say 'good' or 'fine.' Inexperienced bartenders will read this as not wanting another drink. Experienced bartenders know that calling a customer by name and asking if they'd like a refill on their specific drink can produce very different results.

If a customer has to ask a bartender for another drink, the bartender has failed. But anticipating the needs of your customers requires strong relationship management. That means checking in regularly and asking the right questions with actionable language.

3. Don't rush your customers

At restaurants, servers are taught to turn over their tables as quickly as possible.

A table during lunch and dinner rushes is vital real estate. That's why servers are trained to ask, "How is everyone doing? Can I get you anything else?" Those are subtle nudges that say, "If you don't want anything else, I'll get your check so you can leave."

Great bartenders take a different tack.

"Bartenders should never take the approach that a restaurant server does," said Hanten. "In bars, people follow crowds, and keeping people in the seats is a good thing."

Sure, people come in for drinks - but they stay for the community, sometimes for hours on end

"Good bartenders also realize that a good bar is a sacred third place," Hanten said.  "It's not home, and it's not work. When a customer is nudged to move along, they lose their feeling of sanctuary. Also many of the most important customers in a bar might not be the biggest spenders, but they're great connectors."

Adds Hanten: "It's all about long-term customer value."

In other words, it's about building the kind of loyalty that brings customers back - over the course of months, years, and even a lifetime.