It takes guts to get the endless unknowns and oddities of customers. But that’s what salespeople do.

At the end of the day, it isn’t how many calls you make, appointments you go on or proposals you prepare. It’s how much revenue you generate. Some sales are better than others, but every sale counts.

After losing a sale, how many times have you said, “I can’t believe it—I was sure I had that one”? No one sets out to lose a sale, but here are seven proven ways to do it:

Deciding who will buy and who won’t. No one dislikes disappointment more than salespeople. Many come up with a clever little trick to avoid it: claiming they can tell if a customer is going to buy or not.

When you tell yourself you know the outcome before it happens, you just pick yourself up, dust yourself off and move on. But you also don’t have to analyze what you could have done differently to get the sale.

Assuming the sale is a sure thing. Because selling is a tough game, many salespeople believe “the right attitude” can influence the outcome of a sale. If they think the sale will go their way, it will.

Unfortunately, this approach keeps the focus on you and takes it away from the customer. Trying to do both at the same time doesn’t work, according to Stanford University’s research on multitasking, which found that the human brain is built to do one thing at a time.

Playing the friend game. The salesperson’s mission is to present a compelling case, not to make a friend or to feign friendship just to win a sale. Customers can see through such thinly veiled tricks. Nobody likes being used.

More than anything, the goal is to be viewed as competent. If a friendship should occur, it will be after you get the account, not because of it.

Quitting too soon. For serious salespeople, the “Urgent” sign is lit up all the time. Get in, get the order and get out. It’s understandable—commendable, even, because that’s what gets the job done.

But sometimes, you can be too sure of yourself—overly confident. After giving it your best effort, you decide the prospect can’t make a decision or isn’t serious. Three months later, you find out that the person bought from a competitor.

Some prospects put salespeople to the test, checking them out to see if they want the business.

Failing to ask discovery questions. Some salespeople can’t wait to get to the good stuff: their sales pitch. They’ve been through the drill so many times they find discovery questions distracting—a waste of time. That may be OK for new salespeople, but it’s not necessary for anyone with their experience.

The purpose of discovery questions is not only to qualify prospects, but to get them talking about what’s really important to them: their business. If you’re listening, you’re learning. When you do that well, you know what to do to make winning presentation.

Here are four good examples you can try:

• Why did you agree to meet with me?
• What sets you apart from your competitors?
• What changes are going on that affect your business?
• What problems are you trying to solve?

Dispensing solutions. When customers have a problem, they are primed to look for quick, easy, low-cost solutions. You might call them “low-hanging fruit” or, more appropriately, “easy prey.” They’re in hot water and they want to get out. This is why salespeople armed with appetizing and tasty solutions get their attention.

Unfortunately, instant-fix solutions are like pills we pop to take away the pain: The pills only disguise the pain, and it always comes back before long. If there’s a single objective in sales, it’s to empower customers to make decisions that are in their best interest—the ones that result in true satisfaction.

Giving customers what they say they want. “What’s wrong with that? That’s why we’re in business, isn’t it?” No. In the age of the smartphone, there’s no need for salespeople who are merely “transactors”—those who give customers exactly what they ask for, whose function is to scan barcodes and say “thank you.” Robots can perform that function 24 hours a day, more efficiently and at lower cost.

The essential role of the salesperson isn’t new—it’s the same as ever. The sales task is that of the specialist: someone who serves as an authentic resource customers can trust.

John Graham of GrahamComm is a marketing and sales strategy consultant and business writer.