Guests are asked to describe their traveling group when they make a request to book. Not providing that info is my first clue as to how well they follow directions.
However, I’m a kind, forgiving soul, so if they fail to do this for some reason, I always, always ask, for multiple reasons: 1) it provides clarification so that there are no misunderstandings later, 2) it establishes a 2-way communication pattern that will hopefully serve throughout the stay, and 3) it helps me evaluate whether the guest is a good fit.
If the guest doesn’t answer, I decline the request before it expires, with a note that further information is required in order for the booking to complete. So far, they have all rebooked and provided the requested information without complaint.
As far as extra fees go, I think with all of these articles and posts flying around online balking about Airbnb fees, it is emboldening guests to whine about them just as a matter of course. In this case, though, it could be that the $40 extra is being treated as an individual charge, and I believe guest fees are on a sliding scale depending on total booking amount. So a $40 charge may have a 20% guest fee, whereas a $1000 charge may have 12% guest fee. The correct way to determine the new guest fee is to recalculate the total booking amount, and then calculate difference in guest fee. I would hope they would do this correctly, but from what you said, it may be that they are not doing that.
I similarly sometimes end up having issues with highly-sensitive guests with extreme, specific requirements and needs.
I have absolutely no issues personally with these types of guests, as I have my own quirks in this department when I’m a guest (for instance, I really have a hard time sleeping with traffic noise, so I asked to be placed as far off the street as possible).
However, I usually try to redirect this type of guest to hotels, as hotels may be better equipped to serve their specific circumstances. It isn’t so much that I am being snarky, or afraid of reviews, or not wanting to hand-hold, etc. - it is just that I want the guest’s accommodations to be as suitable as possible for their specific needs.