Let’s say you take your work to a venue (gallery, home, business, etc.) because someone has asked to see it in person. After you arrive, you’re asked to leave your art at the venue so that other people can see it. It’s fine to do this as long as you have something in writing.
Always get your art business transactions in writing! In this scenario, while you didn’t exchange money, you did agree to leave a valuable asset in the care of someone else.
The piece of paper (which might be called a loan agreement) you draw up should state your name, the title, dimensions, and value of each piece you’re leaving. Your agreement should also be clear that you retain ownership and copyright and that the venue agrees to insure the work while they have it in their possession.