Your course of action would be a great signal to your sales rep that you are a caring person. Well.... a signal that you are an emotional person.
It is a lot easier for me to offer this advice from a distance, but if you can do this without "loosing your cool" in the process, this might provide your sales person with a valuable life's lesson.
Back when I was very, very young I watched one of my employers do the following. (This was not in the radio business.)
Go see the client. Tell him you admire his/her business experience and wisdom. Tell him you have a personnel issue to deal with and it would be very helpful if he could help you decide on your course of action. Explain that one of your talented employees was treated rather abruptly by a client and you are attempting to figure out how to reinforce the attitude and enthusiasm of this employee, while trying to determine what coaching and skills building training to provide the employee.
By this time your client, unless unusually self-centered and pig-headed, will realize what this is all about. If the conversation begins to get a bit fragile, depending on the nature of his business (does he have employees that interface with customers?) you might ask how he would handle the situation if YOU engaged in personal attach against one of his fine employees.
I didn't have strong skills to calmly carry off such a scheme when I was still in the radio business. I can tell you the day I woke up and realized I had grown into at least a modest amount of ability to do this: My father had died and I was out testing the market to dispose of his estate. I was travelling the same roads I once drove trying to sell advertising and visiting with some of the same people (or their descendants) I had once called on. I was rather amazed at my "cool composure" as I convince people they WERE going to help me evaluate my task.... people I couldn't stand my ground to walk away with a $200 advertising schedule years earlier.
Thin your way through it. If you can do this without getting into a shouting match, you can help your own skills, do something wonderful for an employee you obviously value, ..... and what the hell.... you may do a client a favor with some social skills training while you are at it.
Walk in the door with your mind already made up. And maybe a check in your pocket. If the event goes sour, hand him the check, wish him well, and walk out. I once worked for a guy to groomed me how to handle a client I would be taking over. They had such a match 8 years earlier. Just before I arrived they had agreed that they had proven they could live without each other. They decided they could live BETTER if the worked together. I drew some very nice commissions based on that customer.