Dealing with an angry client
Prospects who react strongly to what you present, even with anger, are going to be more involved and passionate about your offerings.
Source: Sales author Josh Gordon
Sometimes the best strategy is to let them vent. Anger is emotional, not logical. Often as prospects vent anger they will not give a logical reason for it.
If you listen carefully for the feeling behind the behavior, the reason may become clear. Responding to the feeling that drives the anger may get you to the heart of the matter.