How to deal with those customer who are short temper and became very agressive without a reason?

you have to listen him first and to know exactly what do they need and see what product can satisfy thier needs 

tell them the advantage of this product in a short way without talking too much 

dont ever say to them to calm down because thats makes them feel more angry nd get them nervous 

Dear Pradeep,

Handling such customers is problematic especially for the processes that take long time. From my previous experiences I can advise:-

1- Check your processing time and find possible ways to shorten the time required to serve the customer.

2- Try to distribute an explannatory brochures or to show a video in the waiting area that show the steps being performed 

3- Make sure to assign special area and employees for the people with special needs or people who need short-time service rather than those requiring long processing time

4- If the customer gets irritated try to reach to a point of understanding with him (I totally understand your position, however, I need to clarify your problem in a better way to be able to serve your need)

5- Always assign somebody with good communication skills to handle such situations. Not all staff are capable of handling such situations.

6- Upon completing the service, review the process that has been performed with the customer, explain to the customer the reasons for delay in a smart way (ex. I really care for your concerns however we will appreciate if you understand that we have a stressed work environment and we promise to manipulate our processes in the future to meet your needs).

These are some strategies that I have been trying which I hope to be helpful for you.

Best Regards,

Ahmed

Stay calm and try to find out why they are upset and how I can assist in solving any of their problems

listen to them first, then try to catch their attention and explain to them what they need to do....

Let him/her to tell what he/she want or even complaint  just listen and if he/ she finish its your turn to explain or take an action.

you have to listen him first and to know exactly what do they need and see what product can satisfy thier needs 

tell them the advantage of this product in a short way without talking too much 

First you have to let him be.. even if he shouts or whatever and then after his or her aggression, that's the time that you approache him, invite him for a cup of coffee, or even a snack.. and then that's the time that you can ask him or her of what is the problem.