For the most part I don't let anyone borrow anything anymore.
There used to be an unwritten code that whatever you borrow should be returned in as good, or better condition than when you borrowed it.
That ship has sailed.
Loaned a 4 wheeler once, it was returned dirty, scratched up, and had two flat tires.
Loaned a couple of trucks before, came back empty and dirty.
Loaned drums, was returned with a cracked cymbal and broken Tom head.
Loaned out a commercial scale, was never returned, had to drive to person's house, walk into their garage, and take it back despite asking for months.
Loaned a canoe, was told it was stolen, then found in three years later in some bushes behind the person's property.
Loaned a Spyderco GB2 to a colleague, who promptly used it to cut open lime bags and chipped the crap out of it.
Loaned out coolers, never got a single one back.
Loaned a table saw, never came back and the dude skipped town.
Heck, I even paid a "friend" to house sit while traveling, with the instructions to feed my dog and cat, and water my yard. Came home to find a pile of empty beer bottles next to a lawn chair, with the only green plants and grass within the sitting radius of the chair. Dog was fine, cat was missing. Found out later he hated cats.
I have finally leaned my lesson.