3. You decide what I should buy. Evidently, you don't trust your customers to make their own buying decisions, so you do it for them. You don't trust them enough to offer options. Do you think choices will confuse them — or worse, drive them away? Try helping your customers examine the possibilities so they can narrow the choices to the point that they say, “This is what I want.”

4. You push the customer to make a decision. You and your customer aren't on the same page when it comes to urgency. You prepare the proposal quickly, make the presentation, and get a positive response from the customer. You make constant attempts to motivate the customer, but nothing works. The customer procrastinates. Later, you find out the order went to someone else. Pushing customers doesn't work.

5. You don't answer the customer's questions. Salespeople think they do, but they don't. They're so intent on what they want to get across, they don't hear what the customer is saying or how they're acting. Even so, salespeople come away pleased with their performance and pat themselves on the back for the great job they did on the presentation — but they don't get the order.

Related: Do you know your prospect's buy-in question?

6. You make the customer feel inadequate. You don't do it deliberately, and you would be surprised and even shocked if customers told you how you made them feel. It's easy to assume customers have a certain level of knowledge but many don't — due to the rapid changes in every industry, including their own. It's important to remember that you may be better informed than the customer, not matter what you are selling. This makes it easy for a customer to feel inadequate — and defensive. If the person is sensitive, this can harm your chances of moving forward.

7. You don't stay in touch after the sale. You make a point of telling customers that you will be checking in with them from time-to-time to see how they're doing and to answer their questions. You know that's what they want to hear from their salesperson. When you don't do it, you let them down. They fell for your line, and you've played them for a sucker, or so they think — and that makes the bad juices flow. Then you wonder why you don't get any more business or referrals from them.

Related: 8 must-have qualities for achieving sales success

8. You don't follow through. You say you'll get a customer the requested information. Three weeks later, you haven't done it. Then, he reminds you, and you make up an excuse or throw a colleague under the bus. The customer comes to the conclusion that he can't count on you. It's time to realize that such experiences are indelible.

9. You try to impress customers rather than help them. To put it bluntly, all too often, salespeople make themselves the “star” of the show. For some reason, perhaps it's a lack of self-confidence, salespeople feel it necessary to “sell” themselves to a customer by peppering the conversation with success stories and name dropping. All the while, what customers are looking for is help, and you miss the opportunity to make a sale.

10. You don't play it straight. The day after having a car serviced, the dealer's rep called to see if the work was satisfactory. The customer told her that he was pleased. So far, so good — until the other shoe dropped. Then the dealer's rep added, “You may get a call from the manufacturer asking about our service.” That's all it took to know what was important to the dealer. The customer felt the dealer was using him.

11. You offer solutions that are either inappropriate or don't solve the customer's problem. You do it deliberately, and you probably get away with it some of the time. But when buyers figure out what you have done, your credibility is gone and so is the customer.

12. You don't take advantage of opportunities to be helpful. A customer came in to replace an expensive five-year-old digital device he had bought elsewhere wasn't working properly. The sales technician examined it, ran tests, made adjustments, and handed it back to the customer. “Try it now,” said the tech. Sale lost? No. Some weeks later, the customer called and ordered the latest model. By helping, the sales tech got the order.

13. You don't think like a customer. The worst criticism anyone can level at salespeople is to say they don't think like a customer. Namely, they don't take the time to discover what's important to customers, what they don't like, how they make their decisions, and what bothers or worries them. If there's one thing customers want from salespeople, it's understood.

Sure, there are easy sales, but they're the exception. Selling requires patience and sensitivity. Most sales balance precariously between yes and no. Most sales are hard to win. It's unfortunate when salespeople make it even tougher for themselves by undermining their own success.

Related: Are you a highly effective salesperson?

John Graham of GrahamComm is a marketing and sales strategy consultant and business writer. He is the creator of “Magnet Marketing,” and publishes a free monthly eBulletin, “No Nonsense Marketing & Sales Ideas.” Contact him at [email protected], 617-774-9759 or johnrgraham.com.