What is the best way to approach an angry or not interested customer?

In the case of an angry customer :

Remain calm 

Listen actively 

Repeat his concerns to show that you have understood hid problem 

Sympathize 

Apologize 

Offer a possible solution 

buy some little gift for him/her. like keyring, pen, or just  say good words for changing his/her mood.talk to him/ her friendly, change his mood first then offer what you want to offer.

We must know  What he needs and submit it to him

simply on the whole try to solve his problem. Or if not simply pretend to solve it .

Better don't approach him/her when they are angry or not interested, your best of the best proposals will go wrong when they aren't in the right mood. Wait, and then let the things calm down.

Deal your unhappy customer like as you deal your best in that situation

First of all, a customer may not be angry at all times. The anger is an temporary emotion which will subside after a certain time. At the time of your visit, this customer's intensity of anger may have reduced considerably. So handling anger is not a major issue now. The second issue is that the customer is not interested. Now you should try to find out the reason why he is not interested? This can be done by careful implementation of probing skills. if you are able to uncover the reason, then you can handle the situation by proving the features of your product or services can solve the problem to the customer. This is the way to professionally handle such customers.