First one to raise their voice during negotiations loses. Do you agree? Why or why not?

Professionalism and diplomacy are two of the most powerful tools in negotiation, so, CHILL.

Negotiation is a process which calls for calmness and strategy. Raising one's voice does not necessarily mean defeat as it might be a strategy of obtaining consent by intimidation.  It is more acceptable to be calm and well researched than to raise one's voice.  Yet, if the second party does not realize the gist of the high voice they may also fail to articulate the situation to their advantage and lose on a good deal.  So, l wouldn't say outright it is an outright fail.

Loser - raising your voice sends a number of signals to the opposition i.e.:

You are not in control of your emotions,

Your professionalism is questionable,

Offensive behaviour is a big no no,

You can be percieved as a bully,

etc. etc......

Depends on the situation, but surly the worker should have patience with the clients and listen but in some cases he has the right to raise his voice tone to demonstrate the other bad behaviors.

I do not agree, cause raising my voice during a negotiation may lead to more complex conflicts through meetings. I rather stay calm and understand the other person's perspective.

It Depends on the situation. Better to first listen the strategy of the client and then make a proper move.

Negotiation... two way communication for betterment understanding in closing any deal.. Patience and good listener will win the negotiation..

First one to raise their voice in negotiation loses. I agree. This is because the person who raise their voice has a tendency to impose his decision on other party regarding the negotiation which is forceful and made without the consent of other party.

yes , first you have to lestin

As this differs from situation to situation, I would say it is neither true nor false. I do believe it completely depends on the environment surrounding the negotiation, also boiling down to the character & underlying behaviors of those involved. If the surrounding environment is hostile, it would do well to listen to various arguments/statements and then speak as this could prove advantageous.

Jumping the gun and raising your voice first could ultimately backfire if the surroundings are not clearly understood. 

Listening and have patience while negotiation as during negotiation process actually you are knowing the your  product/ service weakness  and competitor strength which is ultimately good to become better or even best .