Be careful not to mirror in a manner that can be perceived as an insult.

I Win You Lose!

Want to get cooperation from your negotiating opponent?  Want to reach a position of balance with your opponent?   Want to eliminate the “one upsmanship” that seems to dominate the typical “I win, you lose” posturing?  Want to keep your opponent from getting the better of you and at the same time, keep you from getting the better of him?

We need to recognize that what's good for one, is typically good for the other.  That balance, that logic is hard to ignore.
So what's the mirror technique and how can we use it.  Perhaps the best way to describe or explain it is to say that one simply gains cooperation from their opponent by matching, mimicking or mirroring every tactic or technique they use during the bargaining.
If they act insulted, you act insulted.  If they get loud and aggressive, you get loud and aggressive.  If they get calm and cooperative, you get calm and cooperative.  It's the simple to understand, easy to use technique of 'doing to them, what they do to you."
It's hard for people to get upset by its use because you're simply returning what you're experiencing.

Examples

During the negotiations or bargaining for the purchase of a new car, a salesman was heard saying to a customer as the negotiations were breaking down,  "I can't believe you're going to miss the chance to own this vehicle for the sake of $300."  The customer replied,  "I can't believe you're going to miss a chance to sell this vehicle for the sake of $300."   How disarming this would be to the car dealer.  If, by his logic, the customer shouldn't worry about an amount as small as $300,  why then should the dealer be concerned about $300?  Powerful.  Easy to apply.  Effective.

You'll see possibilities for the mirror technique all the time.

• When a vendor gets insulted at your low offer, get insulted at their high price.

• When a buyer compliments a feature of a property they're considering, compliment them for being perceptive and observant.

• When a customer says they think they ought to get a concession, ask them to justify why one should be given to them.

If a buyer greatly improves their offer, respond with a significant concession in return dealing with a non-monetary item (time, closing, storage, repairs, items included, etc.)

If a customer says they'll refer more business to you in exchange for a discount, accept the arrangement conditioned upon the realization of new (referred) business.

Good negotiators are adept at mirroring.  They match their opponents when it comes to attitude, proposals and creativity.  Remember, it's taking a technique that your opponent thinks is fair and using that very technique right back on them. Try it.  You'll like it.