I'd loan a gun to anyone that I would loan a tool to. I don't hang out with people that are iffy to me. I have bought guns with the intention that it will be a "loaner". That way, they don't have to borrow some of my finer guns, but I don't let them down.
I have turned people down before, to borrowing a gun. I didn't like the situational they expressed and it made my spidey sense tingle so he got denied. I gave a 38 snub to my sister once because she was about to drive from Ohio to Washington state all alone. I told her to not worry about returning it, I just wanted to make sure she would be safe.
I loaned my BIL my G21 once when he was going camping and had no sidearm. Sure, here ya go. Family. When he got back, he was unloading his truck and the G21 slipped from the holster and hit the gravel. It made a mark on the back side of the grip and he was about to go buy me a new one because he damaged mine. I drove over fearing the worst and I looked it over and seen nothing. He had to point it out to me! He was so worried that I'd be mad and want a new gun, I could see he was stressing hard about it.
That boy was ready to replace it. He respects me so much that it worried him so. I felt really good about that. That he cared so much to do me right and was honest about it with me...and for such a small ding. I slapped him on the back and said hey, it's a gun. You're family. Don't worry about it at all. I'd loan him another gun without hesitation.
I let my mdl 83 out the door once to my friend who was going to the range and I couldn't make it that day. It was more for me because I wanted to chrony some loads and he did that for me. He was very surprised to have me offer him my finest revolver to borrow (but I know he's no bubba, and is over-flowing with common sense). He thanked me up and down for letting him borrow such a fine gun and said he'd clean it up real good before bringing it back. I said no to that, bring it back dirty and I will clean it. Shooting it is one thing, but taking it apart is another matter that I didn't want to take a chance with.