What are the tactics we can use to compromise an angry customer?

The best tactics is to keep quiet until the customer calms down.
An angry customer will not hear or see anything.

As commented, check out their body language and yours, you can make the situation worse by how you approach and stand next to the customer.
Always listen for the feeling word first and not try and get to the root of the problem to quickly.
Once you acknowledge how they feel the anger disappears.
if they say I am really angry/upset, repeat back I can see you are angry/upset.
They will then tell you why, much more calmly.

Listen to the customer, then reply.
Don't argue but help the customer understand your point of view in a matter that will help make the situation better.
And most important focus on resolving the problem for the customer so that by the time they are ready to leave they are fully satisfied and walk out with a smile.

say welcome to him ..
ask him about his problem..
take my step to solve this problem ..and try to take all of his angry and make it happy because he use my company service

angry customers are always there in any business, the best way to compromise there angry is to understand why they are angry, think from there side, " he might be wrong he might be right" , use a proper tone first, choose a proper talking style and try to listen carefully.

Lets the customer speaks and listen carefully and show interest that u r really concerned for him.
Your body language always positive while listen to the customers complaint to support his anger.

Simply , behave as if we are enrolled in a [hidden camera] and you will deal and manage quietly costumer anger which subsequently will drop instantly in reaction to your behavior, from emotional intelligence [ Daniel Goleman]

SOME CUSTOMER BECOME ANGRY DUE TO WITH OUT ANY REASON, YOU WILL HANDL THOSE CUSTOMER THROUGH COURTESY, ASK THE REASON POLITELY, BRING THE COLD DRING FOR IT AND SAY HIM I WILL SOLVE YOUR PROBLEM WITH MUTUAL UNDERSTANDING, YOU WILL GOT A GOOD RESULT.

Tone of speech should be one notch higher than that of the latter.
Secondly, body language and making them comfortable by adding personal experiences in the deal.

Listen to them with respect , try to find a good solution for their problem , Not be angry , we should be careful that don't lost more point ( maybe our customers play angry persons role for get point) we should listen to them and after good thinking .
We Should find a good way to both sides are winer.