What are the fatal mistakes of a sales person during the negotiation process?

Lack of information about the product 

Unable to communicate the information

Not being a good listener 

Try to burn the process and bad listener

Poor listening skills and being aggressive can be fatal during negotiation.

1) Inconsistent statements 

2) Being very aggressive or being pushy 

3) Not being attentive / Causal attitude

1. lack of information about what your selling to the customer
2. poor negotiation skills
3. lack of confidence 
4. poor communication skills

being very aggresive and pushy

In a Negotiation 'A Salesmen' should know the Objective of the negotiation process & understand the 'Buyer's' Perspective before even initiating the process of Negotiation.

Most Salesmen FAIL because:

They forget the process of creation of Value to the Buyer, they forget to realize that he needs to show the benefits of the product, what value it is going to create in the Buyer's Portfolio:

Either it could be increased sales, More outlet attention, activities of the brand (BTL) etc

If he fails to realize this, he already started the negotiation to LOSE ...