You should count yourself lucky it is only body odour. We had an elderly couple stay with us, they were very sweet, but each evening, the husband spent a long time in the bathroom (the guest bathroom is across the hall from the guest bedroom), and the smells were foul. I even said to my hsband that we must have something wrong with the drains as there was a really bad smell of sewage. I couldn't figure out how it happened each evening, you'd think if somone had food poisoning that surely would only be for a couple of days, not every evening (and only in the evening) for a week.
To cut a long story short, we figured out from the items left in the trash after they left that he had a colostomy bag and was emptying it out each evening in the bathroom! I had to spend almost 5 hours sanitising the bathroom to get rid of the lingering smell of s**t, used 2 bottles of Drano in the sink as a foul smell was coming up from the U-bend, it was the most unpleasant bathroom cleaning I have ever done.
Then, stupidly, when it came for me to do the review I felt sorry for him and so did NOT give him a low rating for cleanliness, because there was actually no visible dirt in the bathroom, he was very tidy, he had obviously made an effort to make sure he had rinsed everything down. It was just that the room stank.
Now I'm kicking myself, because in his review, he's given us 4 stars for cleanliness because we only changed the towels once during the week and did not change the bed linen during the week. I say in the listing that linens are changed weekly, they stayed 1 week, so I only gave them a clean set of towels mid-week. I wish now I'd been more ruthless in my review, but hindsight is a wonderful thing.