SB, I am not the respondent you are looking for when it comes to active monitoring of call performance, as I don't currently use it. But I don't think I am altogether out of my league, as I have a management as well as a customer perspective.
From the management perspective: what is the yardstick for not a CSR not providing a pleasant tone, is it all subjective listening with a dash of common sense? Does this person provide a "dead pan" or "lifeless" tone? When you say that there is a noticeable reaction on the part of customers, that invites me to wonder how explicitly you know this to be the case, are you deducing this from tones from customers?
Regardless of the tools in place to determine that someone's "attitude" is not in the right place with customers, your company needs to have the ability to make "upbeat" customer interaction a measurable performance factor upfront. It should not come across as a surprise to this employee that her spoken demeanor is being looked at. When it comes to what is friendly, that is where the true subjectivity ensues, and I will tuch upon this in a customer perspective. The main thing a CSR needs to do in order to achieve a friendly demeanor with a customer is to be in synch with the customer's drift of thought and to manage that drift in an organized fashion.
Customer point of view: I can't stand scripted calls. I feel like I am abiding by extra rules I don't need after I have bought something. The quality of a call diminishes for me when I hear someone ask if there is anything else they can help me with and end with "thank you for choosing _____."
I didn't choose to endure all that canned stuff when I chose to go with that product. All I want is someone who can make sense of my situation and deal with it. I don't want predefined scripts that don't necessarily suit the free-flowing conversation I feel that I need, and the last thing I want is to be expected to fit into someone's script!
Sb, your CSR could very well be lacking in the friendly department, but I can tell you that what I want as a customer is solid information and not scripted phrases that only build on contingencies I can do without. If your monitoring system is heavily script-based, maybe this person has a leg to stand on, maybe not.
But if you're confident in your findings (via the people that listen to the employee), then explain to the person that you need to hear a particular quality subject to seasoned experts that have been through what she is working on for X years, and put the person on an improvement plan and have the backing of Human Resources when you do that. When the person continues with the lack of "objectivity," you would need to emphasize to that employee that performance assessment is a constructed chunk of data and that person is not in position to yea or nay the findings of listening experts that have been where that person is before. Anything further to this conversation would be grounds to getting HR to leap in and be on side with a termination if there is no cooperation.
I guess the question you really had was "what do I do if the metric and the employee's convictions conflict?"
What I said above is what I would do without having a corporate policy spelled out in front of me.