Which means they should know better. And some of them do -- I have a few local favorite companies, where I know they'll keep things together, they're good about finding manuals in file cabinets and putting them with their respective items, etc. I'm usually happy to pay their asking price, because they're interested in seeing the items go to good homes and get reused, and take care accordingly.
But, likewise I have some "un-favorites", one who was notorious for sticking price-tags on screens. I might've finally trained them out of this when I told them I'd only pay their asking price for a particular piece of test equipment if they could remove the sticker without damage. They removed it, the already-degrading plastic screen was obviously fucked by the adhesive, they exchanged awkward glances with each other, and I walked away. Maybe they'll keep that in mind on the next sale they run.
As exemplified by what is going on in the Middle East, the USA has different values to the rest of the world, so don't take this criticism as a slight, just don't come here and expect to be liked for what you are doing.