@Erin74 You asked in your OP if it was alright to leave your dog when you are staying elsewhere, and that's why others responded as they did. If you're spending the night elswhere, I'd take him with you. Now it appears that you are only talking about the dog being loose in the house while you are at work or out on errands?
My dog has also never been crated, she is primarily an outside dog. And she is almost always left at home when I go out- she doesn't like riding in the car, and of course can't be taken into the grocery store. As long as you're clear in your listing about the dog, and him being left in the house when you go out, I don't see any reason for you to crate him. As you say, all your guests have been charmed by him, doesn't seem its been an issue.
As far as guests letting the dog out, I'd make up a sign to post on the door, asking guests to please not let him out. You could explain to them that he's not doing it because he needs to go relieve himself, but because it's his habit to wait for you there.