I unloaded a steel structure on a jobsite, and left the rigging there to set it with the next day. Next day, one of the nylon roundups is all torn up, on top of the structure. Dirt contractor "borrowed" them after we left to move some concrete structures, and put them back on the building. They had to get out a ladder and climb on top of a 10' tall building to get my straps. I asked him if he knew what happened because I had a ruined strap- only then did he did admit to using them, and he knew he tore one up, but hadn't said anything to me after ruining it.
I charged them for the full set of 4 straps, plus shipping for me to get the new ones. I suspect he turned around and charged the general for them, but I don't know and I don't care. I was just glad I noticed the torn up strap, if it would have let loose on my pick, it would have been ugly. To me- it was a pretty good indicator of his character for using them, ruining one, and then not saying anything about it. Just put it back on my lift for the next day and hoped I didn't notice.
That said- a lot of times on jobsites the general contractor will have a telehandler as a rental machine, and we will borrow it (with permission) to move mats or other things on the jobsite. Sometimes its some other contractor renting the machine, but I'd never use one without permission.
I actually don't like borrowing tools/ equipment I don't have from someone else. I'm always worried I'll break their stuff, and not only have to fix theirs, but still end up buying my own to do the job with. If I need it more than once- I need my own.