Fortunately, he only had two of my paintings. To be fair, this is the only time anything bad has happened to me in 25 years of exhibiting. It goes with the territory - no risk, no exhibits. I thought of framing it as a post-modern piece. These are called consignment sheets.
Some galleries offer contracts, others do it on an handshake.
However, you MUST have a consignment sheet. Now and again we see newspaper articles about such scandals. A favorite shady trick of some galleries is to collect the money from a sale and use the artist's portion to pay the rent - putting the artist off. Or selling work and not telling the artist. Very common practices.