Hi @Tim510
This is a popular peeve for many hosts. Personally i feel regardless if a hosts charges for extra people a guest should always ask if they wanted to bring another person onto your property, especially if you are an on site host.
Many hosts, (myself included) put a note in the rules that guests cannot bring anyone else at all (after the number booked). How strictly you enforce that is up to you.
Even with it on my listing, on the rules a guests has to manually agree to before they arrive, and in the very first message i send them, i still get guests who try to bend it 'just for them'
'My friend wants to come and help me get ready'
'They're helping with luggage'
'We need to do evening prayers together'
I tend to be apologetic but reallllllly firm, because for me if they can't respect that they wil probably ignore basic things elsewhere.
That said, people may not realise, a polite word and they could be really apologetic, and arrange to go else where. And yes there are very, very few occations where i've been ok with it. Generally when its family coming to collect them to take them out for the day/ dinner ect. Or someone ones to book an extra person for part of their stay (pre-arranged!)
But you need to be happy with it first, don't worry about the potential for a 4star review if it's making you uncomfortable, sometimes guests need a nudge to remember they are in another person's home