If a customer complains about the service of one of your colleagues, do you agree with him or defend your colleague?

I believe that the best way to handle this type of situation would be first to listen to both parties. Listen to the complaint of the client and than listen to what your colleague has to say about it. 

The best thing is to try your best to be objective and keep in mind the rules and regulations of your company, the client service policies of your company and get to a conclusion. 

Based on your conclusion, you take the appropriate actions. But mainly, you must do your best to solve one way or the other the client's complaint.

I will hear out the client's complain, and apologize in behalf of the company and my colleague, and handle things in a very professional manner. It is not proper to take sides, or at least make it obvious that I agree to either party because having to do so will discriminate either one of them. Costumers/Clients should be treated with utmost patience, although they may not always be right. The best thing to do is to find a solution to their situation: like, if they need some things to be done, or they have an inquiry or whatever then I will assist them if needed. As per my colleague, I will speak to him/her if necessary regarding the situation that had occurred after I finished with the client, or after working hours, or during break time. If such complains were required to be logged, which usually it is the client who signs up the papers of complain then I will follow the protocol as per the company procedure.

Well, best thing to do is to not to intervention in this as a colleague, you can ask the customer to help him if he didn't like your colleague services, or ask him if he need to see the manager or the supervisor to resolve the issue! 

regardless to whatever happens, customers are always right.To handle such a a customer  complain ; we should start by apologizing to the agent and make them calm down and start asking them about the problem and listen to their stories, not only this try to say some jokes in between then tell them the solutions they have and fix it for them by giving different versions of solutions.

First you have to solve client probleme than if you are your colleagge supervisor you can advise hime but never give advise when the customer is there you must be alone you and your colleagge You must be whith your colleagge .

agree to customer and upgrade the colleague

First I will listen to guest  and will apologies on behalf of my colleague for inconvenience.Then i will try to solve situation. 

I will not interfere myself if customer is complaining my colleague instead i will let my supervisor or manager to talk with the customer to solve the issue in a proper way. 

First of all apologize for what happened to him & tell him that you will check with your colleague  about the issue and advice him. Presently take interest in solving  the actual need of the customer, if it has not been sorted out!! 

First the details will be discussed with the customer and my colleague.  If the problem is from my colleague side, then we would apologize and take further steps to satisfy the customer needs.

Listening to both sides first before taking actions. But regardless of who's right or wrong I will not argue with anyone. If I myself as Team Member can resolve the problem I will help them by giving possible solution but if not, I will report it to my superior.