What are the common mistakes every sales person will do?

1st that he not be in time . use his body language too much  

Nicely elaborated. I believe committing mentioned mistakes creates a big difference between a mediocre and a professional sales person.

There are so many mistakes even more than mentioned by colleagues, I can add some such as:

TOO MUCH talking, lying, assuming, promising, expecting, selling, joking, pushing, 

1.They talk instead of LISTEN

2.They presume instead of ASKING QUESTIONS

3.They ANSWER UNASKED QUESTIONS.

4. They fail to get the prospective client to REVEAL BUDGET up front 

5.They make TOO MANY FOLLOW-UP CALLS

6. They prefer "MAYBE" instead of getting to "NO"

7.They work without a SYSTEMATIC APPROACH to selling