I have lent a bike to someone. Initially I was helping a woman I met by sheer accident to get fit enough to do a long cycle ride. It was 88 miles with several passes in Wales included after s mostly flat approach. But she hasn't ridden since she was a child. It was for charity. We met by chance whilst my husband and I were walking along an old railway line (converted to cycleway walkway etc). She had a flat tyre and couldn't fix it. We were about 200m from our house so took her there and fixed it for her. As we were chatting we found out what she was doing and I offered to help her get fit again and accompany her on the rides, but not the charity ride itself. My husband did that. She was terrified of roads initially. About 4 weeks before the charity ride itself, her old bike failed permanently. She couldn't afford a new bike or anything that was fit for what she was doing (and the others doing the ride with her were all men with much larger bikes than she could ride or only had the one bike). So I lent get my road bike and taught her how to ride it, how to corner, use the brakes, even change gear on it. It was about half the weight of what she had been riding so I soon had her riding much faster than before and climbing much faster etc. on the day, I lent her some locks, spare for repairs etc. She needed none of them and completed the entire ride (she did try quitting close to the end but my husband ignored her because it wasn't a safe place to stop so cycled on to somewhere safe and by the time she got there she was over her little tantrum and ready to eat something and continue).
So yes and yes my bike got damaged when she fell off it, I always knew it was a possibility. I didn't know her beforehand and only one her for about 8 weeks before lending her the bike, but I would do it again.