@Tad162 Just leave general , brief comments, rather than details. A bit of trash strewn around, if it was generally left clean, is no big deal, some guests are just messier than others. Comes with the territory. Maybe something like " Extra, unbooked guests snuck in during the night, did not respond to messages, linens stained beyond salvaging. Unfortunately, cannot recommend."
And thank you for wanting to warn other hosts. Too many hosts are reticent to be honest when it comes to poor guest behavior. As a non-IB host, I cannot see guest star ratings- we rely on written reviews.
If you haven't already, really research stain removal methods- if the correct product is used, most stains will come out. I've read that acne medication is one that seems to permanently stain, though.