I've loaned out basses to friends in big bands, with no problems (Jamiroquai, Aswad, Rod Stewart, etc, etc). Nice guys, who were appreciative of the help, and who looked after the instruments.
Sometimes, however, the user can be a bit "amiss" in their care of the borrowed bass. I loaned a bass to a player in a BIG group (probably as big as it's possible to get), and the bass arrived back home with dents on the back of the neck, and the nitrocellulose lacquer chipped off in a few places. Looked like it had been clumsily rested against the edge of a table top or similar on more than one occasion. I had to steam the wood dents out, and then re-finish the rear of the neck.
Oh well, one of those things I guess.
It's no fun when your well looked after equipment takes a beating from someone else, huh?