Sounds as if you are pretty "inexperienced" on this topic. Anything can happen when it is being handled by someone else. Also, you don't know if the borrower has a coating of dirt, oil, lotion, or whatever else that affect the strings.It's a bass, not a holy grail. How in the crappie can someone hurt it by playing it? Some of you people are weird.
About the only thing I would have made sure of is that he didn't mess with the volume knob on my amp. Heck, even if they tweek the amp it takes me seconds to get it back where I had it.
I don't see the big deal at all. If you kwn a bass someone can hurt by playing you need a different bass.