I feel extremely pleased with myself when I’m one of the 37% of 243,289 respondents who got an answer right!
Correct commalizing is counterintuitive: if it’s done right, it appears that you’ve used either too few or too many, while the number that “feels right” usually isn’t.
Then, your best bet is to use too many half the time, too few half the time, and don’t even worry about the other half.