I like sellers to be as accurate as possible. If seller "knows" it's HUO, regardless of proof, that's fair to say. And it's fair for me ask how they know this. It doesn't mean I have to believe them... it's still a buyer beware situation and inspection overrules everything, but I do want to know what the seller knows.
I'm not sympathetic with sellers using the term if they can't possibly know for sure.