I've come across two very different explanations of fogging. The first describes it as an assertive communication technique with the following definition:
Fogging consists of finding some limited truth to agree with in what an antagonist is saying. More specifically, one can agree in part or agree in principle. (From Wikipedia)
Fogging is an assertiveness skill that is aptly named for the dense mist that has often confused many travelers. In a fog, we lose our bearings, miss important landmarks and find ourselves off the road in a ditch that we failed to see. The assertive communication technique of fogging works the same way by confusing the verbal bully, who expects his victims to get angry and defend themselves, entering into a fight that the bully knows all too well how to win. Fogging works because the technique presents to the bully a tactic they don't expect: agreement. (Bert Webb).
A second definition focuses less on creating or verbalizing AGREEMENT, and much more on confusing the other person by throwing up all kinds of irrelevancies so they lose track of what they are saying.
Merits Of Finding Agreement With Angry Customers
Finding areas of agreement with an angry customer, and verbalizing those agreements have a lot of power, particularly when customers don't expect the "victim" of a verbal attack, to actually agree. I teach this to customer service representatives in my seminars, but I call it the "You're Right" technique, which focuses on the agreement, rather than the confusion.
Problem With Intentional Confusion of Customers
If you intentionally try to confuse an angry customer, (and it can be fun to do that), you can end up being as manipulative as the difficult customer. That's not a constructive or appropriate way to treat anyone, but worse, in a customer service setting, frustrating a customer will escalate the anger, or emotional response.
Focus on the agreement, and pointing out any areas where you and the customer's views converge. Look for and mention the common ground. THAT works. In fact it works so well that it's used often in hostage negotiations. Confusing someone is NOT used in the same way in that same setting for obvious reasons. Confusiion causes frustration which escalates anger.