Hey Primocards,
There are a couple of factors here:
- The "on-page grade" you got was from Moz's crawler, and they're very specific about exact matches. On the other hand, Google's crawler tends to be more loose. Moz doesn't futz around w/ variations with punctuation, plurals, etc. And yet Google will know that "men's" and "mens" are fairly similar.
- I have noticed that Google does have different rankings for slightly different permutations, e.g. "printing company" vs "printing companies" can lead to a local (with local packs) versus a national search (no local packs)
- Then there's the grammar. I'd say that "men's" is the more accurate, and that may have a small (IMO, the effect is probably very small) impact
tl;dr; change it if you can, otherwise, don't worry about it. If you just want to improve the usability your Moz reports, just change the keyword you're grading from "men's" to "mens".
