@Janelle21 You have a guest who is basically like a teenager (maybe he is only 18 or 19?) and doesn't understand that wet towels can't be left on a leather couch or that the unwashed chicken tray isn't okay to put with clean dishes. There really isn't much you can do about that except clean up after him, because, as you say, you'll just be nitpicking all day. His mommy probably cleaned up after him.
Slamming the doors is different- that is disrespectful to others and you should ask him to be respectful of the fact that he chose to book a home share and not create that kind of noise that disturbs others. Also that he can damage your door by doing that and if that happens, you would need to charge him for repairs.
I'm also a home share host, and about all you can do in this situation is change your own attitude so you aren't so bothered by his inattention. Pretend some young nephew or cousin came to stay with you and behaved cluelessly like that and just resign yourself to having to pick up his wet towels, etc, because no one ever taught him any different and you won't be able to teach him that in a week.
You don't indicate what sort of person he is, if he is easy to converse with. In some cases you just need to be real. "Dude, (as she pulls at her hair) you are driving me bonkers- did your mom just clean up after you all the time? I really hate to have to nitpick at you, but could you please try to be a little more conscious of the fact that you're sharing my home with me and not living alone?"
Make sure to leave an honest review. One thing I'd say in the review is that he isn't suited to home-sharing.
Either put up with his unconscious ways, and try not to let it upset you, or tell him he has to find another place and leave.
I had a guest who was a totally lax dishwasher. She cooked a lot, and always cleaned up the kitchen after her meal prep and washed her dishes, but there was always bits of food and grease all over her "clean" dishes. Unlike your guest, she was a totally delightful person and a good guest in every other way, so I chose not to mention it (although I'm sure she wouldn't have been offended and would have paid more attention if I had), I just rewashed her dishes when she wasn't around.