@Jide-And-Michele0, @Florian-and-Theresa0 @Margaret0 - I agree with @Dave-and-Deb0 - when a guest books a 'P' private room, it is that, Private.
Personally, I would not enter the room of a guest unless it was a matter of urgency such as a fire alarm going off or if they were playing music at a horrendous level late at night and i couldn't get a response when knocking.
If you are viewing the room to potential guests or long term renters or purchasers - you need to do it when the room has no guest staying. I guess if you informed them 'before' they booked and they were agreeable, then that's OK. If sprung on them on arrival, IMHO, it's not OK -
Asking a guest to keep their room tidy when only they are in it, I personally feel is not necessary since it doesn't disturb anyone else. Shared kitchen and bathroom is a different matter.
My place for guests is a full-equipped, pretty much self-contained apartment on one floor of my house with their own street entrance etc etc - on occasion when a guest has asked for assistance with something that requires my entering their apartment, I turn a blind eye to clothes strewn evrywhere, unmade beds, pile of washing-up etc (particularly when four girls are staying) as it doesn't concern me at all. Just so long as they leave the place clean and tidy and undamaged when they leave.