I do exactly the same as Sandra (sorry, can't tag you, Sandra), although luckily I've had quite tidy guests. I have a 3 night minimum stay, 2 weeks maximum. If a guest stays longer than a week, I'll offer them clean sheets and towels at the halfway mark and ask if they would like me to change them out or do it themselves and all have said they would do it themselves. The only time I ever entered the guest bedroom/bath was when it started raining when the guest was out and I had to close the windows, and when a guest requested that I vacuum up a spider that was on the ceiling of her room.
I leave a broom and dustpan in the guest quarters, which I know they do make use of occasionally, as it's impossible to come home from the beach without bringing sand with you, which is unpleasant to walk around on in bare feet.
Hosts who do longer term bookings often suggest to make a policy which they state in their listing and to the guests on arrival that they go in to clean and change out linens once a week (arranging a time that is suitable to both host and guest), which gives them the opportunity to make sure the guests aren't living like pigs in there, remove any leftover food and overflowing trash and be able to mention to the guests that they should please not leave the heat turned up full blast with the windows open, for instance:-)