So the reason this happens a lot is the nature of rental equipment. A lot of the times the renter isn't there while the gear is being dropped off or picked up, so there's no chance for an in person key transfer.

Reasonable people use one of those magnetic key boxes and then send a text/email giving its location, but either hanging in the ignition or under the seat are absolutely the industry standard

Multiple times over the course of my career have I a "borrowed" a random forklift when I needed to move some thing and mine either wasn't available/had not been delivered/ran out of power.

Yep, I work in industry where I'm constantly dealing with rented industrial equipment and I have a zippered pouch with like 75 to 100 random keys in it that I've accumulated over the years. I have never fail to be able to start any piece of keyless equipment that have I come across so long as it's something I've rented before.