1. Trying too hard. A salesperson can be so focused on making the sale that customers feel pushed to make a decision. Even though they may want to say yes, they say no instead as a way to escape.

2. Inadequate preparation. Using “canned” or rote presentations that are so general they're meaningless and emphasize the product or service without reference or relevance to the customer.

3. Ignoring the customer. Customers try to figure out whether or not a salesperson is genuinely interested in them, and the answer determines the outcome of the sale. Any answer other than “yes” means a lost sale.

4. Talking too much. When salespeople don't know what to say next, they cover it up with more talk. Instead of using such moments to ask questions, they try to get on track with more talk, but it's too late, the sale is dead.

5. Laying on the jargon. Some salespeople think it makes them seem more confident and competent if they use a “secret language” — jargon — to make themselves sound like experts, when it only makes customers feel uncomfortable.

6. Poor follow through. By placing the top priority on closing sales, little effort often goes into preparing the way to get there, including a failure to answer emails, making mistakes, not returning calls, forgetting to send requested information, and not meeting agreed upon deadlines.

7. Writing off prospects. How many times has a prospect become a customer long after the salesperson has dropped them? There's no telling how many more sales a salesperson can make just by staying closer in touch with prospects.

8. Lack of enthusiasm. Whether it's a clerk at a dry cleaner store, a server at a restaurant, a loan officer at a bank, or any other salesperson, it takes energy and enthusiasm to engage customers.

9. Not painting verbal pictures. Too many salespeople try to impress customers with “war stories,” and present “facts” when the customer wants to know how their purchase will change or improve their life, help them feel better about themselves, and fulfill a dream.

10. Playing a role. It's never deliberate, but it happens. A salesperson's words, manner, and attitude can cause customers to react negatively. Instead of acting normally, they come across as if they're playing a part or following a script.

11. Failing to involve customers. It's not only inexperienced salespeople who are guilty of talking to customers, not with them. It's as if they are determined to grab the reins and keep control at all cost; akin to winning the battle but losing the war.

12. Too focused on what they want to sell. It's one thing to be enthusiastic about your product or service, but it's something else to make customers feel what you're selling is all you care about.

13. Stopped learning. They're frozen in time, most likely at when they first went into sales. Customers view them as “dated” and out-of-touch, unable to help anyone meet current challenges and opportunities, and it gets worse with each passing year.

14. Believe they can sell anything. Not only do they believe it, they see it as a badge of honor and a sign of superiority. They brag about it freely in a self-serving attempt to put a shine on a faltering sales career.

15. Impervious to criticism. They guard their self-image at all cost, requiring endless praise for their sales prowess, while striking out at the slightest sign of criticism. They not only deny the accusation, but they also label them unfair and wrong, nothing more than signs of jealousy.

16. Not feeling valued. Everyone deserves a pat on the back, but salespeople, unlike others in a company, can quantify their performance; they know how they're doing. Being disturbed by a lack of appreciation only distracts a salesperson from getting the job done.

17. Overestimating their competence. It's common for most people to avoid bragging by underestimating their capabilities and failing to give themselves the credit they deserve. With salespeople, it's just the opposite. They are prone to exaggerate their competence, their ability to work collaboratively with customers and to close sales.

18. Getting pumped up. No salesperson can become successful merely by listening to motivational messages, attending seminars, or buying the latest sales guru's book. Success takes focus and hard work.

19. Talking down to customers. Some salespeople intimidate customers so they can better seize and maintain control. Some customers acquiesce, not feeling up to challenging the salesperson, while others bail out and go elsewhere. Even those who concede harbor resentment.

20. Putting the brakes on. After a salesperson has been in the business for a while, even some years, they start to put their foot on the brake. Seemingly, they decide to only go so far, letting it be known what they will and won't do. They want to decide which prospects they'll work on, and the level of service they'll offer customers. It's a great way to put the brakes on their sales.

21. Distancing themselves from the company. This is subtle, but customers pick up when salespeople drop hints that that they would do something differently if they were in charge. It's an effort to earn points by showing they're on the customer's side. It almost always backfires; customers don't want to do business with renegades.

22. Confusing talk with action. Because salespeople tend to be verbal, they think that when they say something, they're doing it. They readily agree to get a proposal done, make a delivery, assist with a project, or make a presentation. When the due date comes around, they're absent. And so are their sales.

Selling is hard enough without being weighed down by attitudes and behaviors that make it tougher — and sometimes impossible — to make more sales.

Related: Better selling: 10 tips, from prospecting to closing