Same! I find it mostly amusing, especially the ones whose Air photos and profiles indicate a partner. It was these extra guests all the time that led me to just no longer charging an extra guest fee. I was tired of feeling ripped off by it, so now I just turn a blind eye. If they have four people in one bed I don't care so long as they damage nothing and disturb nobody.
I've often seen hosts feeling disappointed that they gave a low-occupancy discount only to find the guests filled the place. Simple solution for me was not to give the discount. If I had a sleeps-8 and they only bring 4 people, they'd be paying full price at my property, it's not worth the angst to offer discounts.