What is mutual exemption?

The "mutual exemption" here is actually literally free, but there are multiple meanings behind it. Coser usually asks photographers to pay for photography, but some girls don't have enough money, so they look for "mutual photographers". These "mutual photographers" are usually newcomers and need to practice their hands. They need money to get coser to shoot it. Therefore, the "mutual exemption" here means that the photographer shoots for coser for free, and coser models for the photographer for free, and the two sides reach an understanding of * * *, and other expenses incurred in the shooting process are self-care.