Lets’ face it, all business owners will have a fare share of complaints and bitter experiences their customers had with your company products, services or worst, both, or even the front line staff. Whistle blowing is another more serious matter for any wrong doings by any rank in the company.
We have a fair share of our bad days, but that should not be an excuse for us to show our impatience. You want your team’s direction to be aligned, everyone’s action or word, no one is to drop the ball.
It will start off with ” I want to speak to your boss” and you may not be there during then.
Look at it positively. If he wants to see you, he wants your company to improve and he bothers to feedback to you. The other end of the stick is he will just walk away and your competitor will welcome him with open arms and worst, you don’t even have a chance to explain.
Our suggestion is to have an email made known in your website , example feedback@your_company_name.com or wecare@your_company.com. Let your customer know that this email will reach the management and all correspondences will be kept private and confidential.
Our email is firstname.lastname@example.org
Another group that may feedback to you is your vendor that deals with your managers at operational level and never have a chance to meet you and they have grievances to share with you or whistle blowing your staff.
As your company grow, you may not be able to be at all the place at all the time. Provide an avenue for anyone who want to get your serious attention. Usually people will go to your web page to click on [Contact Us], place all your email there , example
Make it obvious that they can only choose  to file their complaint or compliments.
Or unless you are willing to let this customer go ( note that customer is not always right), listen to what they have to say and give an appropriate response that will save your company reputation even you may not be in the wrong and you do not want to go there