Whether you are new to Sales, or have been selling for 30 years, a true Sales professional must always guard against these 13 deadly sins:

1. Winging it.  Don’t be too confident that just because you know your product inside-out, and may be working for a market leader, that the buyer will simply sign on the dotted line.  Plan, focus, and prepare for each sales interaction.
2. Judging a book by its cover.  Never assume that you know the buyer before you’ve met her.  Sure, you may have sold 100 buyers like her in the past but no two buyers are “just” like another.  Take the time to learn what’s different.
3. Careless.  No one likes a careless person. It takes several forms from sloppy hand writing, to inappropriate dress, to bent presentations…just plain old messy.  If you don’t care, why should your buyer? Be neat. Be presentable. How you present your whole self shows the buyer your respect for yourself and for him.
4. Being late. Don’t be late…ever.  Traffic isn’t an excuse.  Sure there’s a late plane, train, or bus.  The unexpected accident you get caught up in.  But normal traffic is not a reason to be late.  Plan accordingly.  If you’re on time, you’re late.
5. Being uninformed. Shallow?  Ugh. People don’t want to interact with a sales person who brings nothing else to the table other than the product they’re selling. Take the time to be aware of your surroundings and world happenings.
6. Relying too heavily on your company’s brand.  Don’t assume because you’re the biggest you’ll get the business. No doubt some companies spend huge resources on building their brand. You can either leverage it and get the sale, or assume it, appear arrogant, and lose the sale.  Earn the buyers trust…you + your brand.
7. Not identifying all the contributors to a buying decision. Your contact may not have all the power. Too often I have seen mountains of effort placed in developing one relationship only to find there were others providing input to the buying decision I had not met, or invested in.  Know those who will be a part of the buying decision.
8. Unadaptable, inflexible.  Don’t let your presentation, or agenda, become an anchor. Years ago my boss and I traveled together to do a presentation to a big prospective partner.  Within the first 5 minutes the buyer changed directions. Much to my boss’s surprise I ditched the presentation, adapted, and won the business due to my ability to flex with my buyer’s changing needs. Have one, but don’t become married to your agenda.
9. Stretching the truth. Just don’t do it. Don’t lie, embellish, exaggerate.  Making promises you, your company, or your product can’t keep is a sure way to kill both your personal brand and your company’s.
10. Competition bashing. Never badmouth your competition…even if the buyer tells you they said something bad about you. Defend it but end it.  When working for Paychex, the founder, Tom Golisano, provided a stern warning for any sales person caught badmouthing its competition. He believed if someone had to sink to that level to win the business the company probably didn’t deserve to win it in the first place.  Take the high road…always, win with respect.
11. Knowing it all. Don’t be a know-it-all. Buyers don’t expect you to be omniscient. A little humility goes a long way in earning trust and respect.
12. Knowing little or nothing. Invest your time to learn what it is you need to know about your company, product, and industry.  Your company can’t, nor should, do it all.  You’re responsible for your knowledge, and accountable for your results. 
13. Talking too much.  You can learn a lot more about your buyer by asking great questions and sitting back and listening to them answer.  We demonstrate respect, caring, and professionalism by listening.  Remember, two ears and one mouth for a reason.

Let me know if you have a deadly sin to add to the list.