John Treace wrote the book on sales management.
Literally (see here).
And over decades of sales, sales training, and management experience he found a common thread among all top sales people:
Top sales people welcome complaints.
Time and time again he found that the best sales people he always worked with and managed never shied away from criticism or became defensive when they encountered a complaining customer. Rather, top sales people always welcome these situations.
Surveys have shown that when customers complain it signals that they actually want to keep doing business with the company if the problem is addressed and resolved.
In my own career with sales I have found that on the rare occasions when someone was upset with something they bought from me, time and time again if I just treated them with respect, and patience, and cleared up any misunderstandings, they came back to be recurring customers with me.
Not just one or twice, but almost every single time I ever dealt with a complaint.
My temporary discomfort with them actually made them a raving fan.
And all it cost me was some listening, a level head, and a true passion to fulfill their needs in an appropriate way.
So attack your business with a servant's heart and a desire to hear out any complaints; it may just turn into big profits in the long run.