If you're creating the file you upload to KDP yourself, not trying to specify a font is the best plan. The defaults should never create an issue like this.
If you're using something like Vellum, that also seems to work. If for some reason it didn't, I guess there is a Kindle setting that allows a reader not to use the font the publisher designated. (I've never had to use this setting; I've only read about it.)
I haven't tried D2D's free formatting tools, but as far as I know, that should work, too.
In the case you're describing, I'd see if the author has contact information on his or website and get in touch if there's an email address. Possibly, the author has no idea there's a problem. You might get the issue fixed that way, and it's a friendlier approach than filing a quality issue with KDP.