@Paul1731 That's strange, because Airbnb lets guests leave reviews all the time when they haven't actually stayed. Their review policy is that if you cancel day-of check-in, you can leave a review. It's a huge source of contention for hosts, because while you being able to leave a review would have been warranted in this case to warn other guests (and all the good hosts out there would like these unacceptable places delisted, as well, as they give all hosts a bad name), that also opens the review door to those who haven't actually even been to the property.
The problem for hosts is that there are guests who cancel day-of without actually having set foot in the place (maybe a friend or relative offered them a free place to stay or they just changed their mind for some reason). Then they get to leave a review which says the place is filthy or some other lie, as retaliation because they wren't able to get fully refunded according to whatever cancellation policy was in place.
But guests like you, who actually arrived to find the place disgusting, should be able to review.
Like I said, I'm surprised you weren't, because it happens all the time.
When reading reviews, as a guest, you have to determine for yourself by reading the reviews, what's actually going on. If a place has 15 reviews saying the place and the host were lovely, and 1 review saying it was filthy, that bad review is probably a revenge review given for reasons like I mentioned above, and you can discount it. If there are a few bad reviews among a few good ones, especially if they speak to the same issues, like cleanliness or host communication, I'd listen to the bad reviews and pass.
Also, reviews are not in chronological order. So there may have been some issues when a host first listed, which they've corrected, it's hard to know.
Star ratings aren't reliable because they are so subjective. Written reviews are much more telling.
It's also better for guests, if uncertain re reviews of a place, to send the host a Inquiry first, ask some questions, see what kind of response you get. If they have some reviews which mention cleanliness issues, ask them if those things have been addressed. Depending on the answers, the tone and the timeliness of the response, you may get a better sense of whether you feel comfortable booking there, before committing.
Sticking with Superhosts and staying away from property-managers with scores of listings may also help to find acceptable accomodations. Smaller, traditional hosts who are either on-site or manage their listing themselves are often much more attentive to making sure guests will have a positive experience.