Going with the customer's energy flow is a verbal self-defense technique because it uses the customer's negative energy to help calm him or her down. It was suggested by a young participant in one of my defusing hostile customers seminars.
The participant, who spent a lot of time working with horses, noticed that there were times when trying to calm a distraught horse down by talking soothingly and calmly didn't work. What she noticed was that if she walked the horse, it would quickly become more relaxed, presumably because the physical activity allowed some of the negative energy to dissipate.
In the same way, there are situations where it's not worth trying to calm down a customer with words. Better to go with the energy flow, and introduce some kind of physical movement.
The technique will work best if you can engineer some kind of movement or walking for the customer, so it's best suited to situations where one is out of the office (e.g. situations where one visits the customer on his or her own turf, and where there's some way of creating some physical activity.
It's simple. Invite the upset customer to move -- to walk, or lift something, or in short, just to MOVE.
Not only can that allow some of the energy to vent out, but it also serves as a distraction -- moving the customer's attention to something other than his or her unpleasant emotions.