How do I know if I am going overboard with the use of negotiation tactics? –Ms. Conscience (Metro Manila)
Before we digress into negotiation philosophy, let me first console you with the fact that you are not alone in this left-right brain dilemma. I reckon you are in quandary between your organization’s drive to win and your personal sense of fairness.  It’s good to know that you are at least asking this question and that it is still a matter that your conscience is dealing with.
However, are we being altruistic, dogmatic and uber-naïve to think that negotiation and human conscience intervention can coexist? Is this fusion at all possible? Or do we have to suspend one to be effective in the other, sort of like some kind of situational compartmentalization?  To have a definitive answer, let’s first understand what dark side negotiation means.
For the benefit of our other readers, let us contextualize the question. How does this position to strike below the belt happen in negotiation? More often, the opportunity to excise a critical deathblow upon your negotiation counterpart presents itself when the following elements meet:  1. a significant imbalance of power is in your favor; 2. you are fully aware that your counterpart has a terribly poor parachute option; 3. you possess lethal knowledge and dexterity in deploying multi-headed gambits; 4. your negotiating style prioritizes a win outcome on your side regardless of how this impacts the other side and 5.  you have a strong killer instinct fueled, or better yet, grossly intoxicated with the addictive taste of the power-to-punish potion.
How do you know you have crossed over to the dark side? The use of gambits alone per se does not automatically make you a “Darth Vader,” as referred to by some of those I have trained in the last quarter of a century.  Some gambits are grey while others come in different shades in between grey and black.  Likened to Star Wars, the Hollywood legendary blockbuster, “only a Sith speaks in absolutes.”  Just like the rainbow, negotiation tactics fall in between a whole spectrum of colors and shades.  
Nonetheless, put bluntly, you will know you have crossed over to the dark side when you have deliberately forced your counterpart to accept a win-lose deal despite options to arrive at win-win solutions in the presence of the five or most of the stated aforementioned dark side characteristics. Apart from gut feel, a surer way to ascertain such is to use the Mansmith Mathematics of Negotiation, which comes indispensably handy during  concession management and determination of outcome valence (win-win, win-lose or lose-win).  This can be best learned in a Mansmith course offering entitled Effective Negotiation and Influencing Skills.
Imagine yourself on the receiving end of a dark ploy that leaves you in undignified mercy of your counterpart. How would you feel? Wouldn’t you espouse remorse over the transaction and most likely with your counterpart? Will this feeling not fuel an opportunity quest to exact a tantamount if not an even bigger amount of flesh?  Would you not cherish and relish unleashing your own scheme of revenge when the table gets turned? For most negotiating personality-types, the answer is predictably a resounding yes!  Thus beware of retribution as a “check for the imbalance.”
In spite of Mansmith’s injection of science into the art of negotiation, inception of values permeate its teaching of negotiation.  The tactical tool, the strategic nego-map, the key proprietary frameworks and processes have all been designed to seek multi-perspective wins as the default outcome. Hence, we strongly believe that the more people we train in negotiation, the fairer this world will be.
Yes indeed, negotiation effectiveness can be attained and better yet sustained with a multi-perspective win mindset.  Taking over advantage of your counterpart will predictably boomerang.  Whatever short term gains there will be will just be nullified in subsequent deals and much worse, will catalyze relationship friction, whose wounds take a long time to heal. 
Rowen Untivero is a Partner and Chief Sales Strategist of Mansmith and Fielders, Inc. and is the developer/training master of Selling Science and 3 Negotiation Courses (Tactical, Strategic and Language of Negotiation), where related framework, processes, strategies and tools can exclusively be learned. Please send your questions, comments or feedback to, visit www.mansmith.netor text 0918-81-168-88.