What is the best way to deal with customer complaints?

 Positively respond to his inquiries and requirement.

Thanking you .

• Try to remain calm when dealing with a complaint - even if the customer becomes irate or confrontational. Complaints should always be resolved as quickly as possible 'cos that is your role/responsibilty & you are paid to do that activity. You better be good at it. I know it sounds easy but that is how things are.
• There are times when 'the more patience you have the more they use it'.

Listen to customer complaints and quickly find solutions to them

Listen your customer carefully 

Give your very best and understand sincerly what and why he/she is complaining?

Apologize for the inconvenience and compensate in such good manner

let customer feel that you absolutely on his/her end and assure that this won't happen again.