I don't think many hosts necessarily mention the extra guest fee in the text of the listing @Ann-Marie113
You input the extra guest fee in your pricing structure, and the guest searches your area for the number of guests they're bringing. Your listing then comes up at the correct price for that number of guests.
It does happen that guests sometimes enter the wrong number of persons. When you see only one guest on the booking, there's a chance it may be wrong (unless the guest mentions being just one person), as going directly to a listing defaults the number of guests to 1. For this reason, many hosts confirm the number of guests in a follow-up message.
@Lorna170 has just mentioned in another post that she always states the number of guests and pets in her first reply to a booking, to make sure the guest booked correctly. If there's any error, you can go to "Change Reservation" and correct the number of guests (which will send the correct price to the guest, according to the extra guest fee).
I'm not saying you shouldn't mention the extra guest fee in the listing text, but the above is usually sufficient. I agree with you that mentioning it can be tricky, as it may encourage an understated guest count.