@Yee0 Hi Yee, Your listing is quite specific! Your apartment is listed as accommodating 8 people! You state that your tarrif is for 6 people accommodated in 3 queen size beds, and you also state that additional people can be allowed for in relocatable beds for an additional $30 per mattress per night.
I cannot see any ambiguity in your listing, and I would suggest this guests is using the time honoured 'bartering' system in order to get something for nothing. How you approach this is up to you Yee, but you are absolutely clear with your listing as to what you offer...cheers....Rob