Edge cases exist, but when I’m sad, I just stop being sad at work, because it’s been clearly stated, from the first interview, that positivity was a requirement of performance.
One edge case: colleague lost her mother last year, of course we didn’t expect her to perform excruciating emotional work.
No one is positive and happy all the time and having to fake it "as a job requirement" sounds wrong on so many levels.
As an aside: I assume that you know this from your own life, and appreciate when people behave in a manner that cares for the emotional commons of wherever you are. Is your objection to it here the fact that it's a giant stupid company ostensibly trying to curate your feelings, and that's annoying and (probably) hypocritical? Or do you really object to the premise?
My proof that I did well at it was that management constantly told me I need to upsell more and tried to scare me into it, but at no point did they ever actually move to take me off the sales floor. They knew I did really well, even without their extra BS items to push.
I did not fake "happy happy joy joy," but I also did not allow self absorption to inject my mood into my business. My model is that sales is a career that involves having structured communications.
That was a lifesaver for me when feeling depressed, because I could focus on the structure of what needed to be accomplished rather than the unstructured touchy-feely business of "getting along with people."
I suggest that "YMMV." Salespeople are not all the same, and some break preconceptions and stereotypes hard while being successful at what they do.