Wouldn’t it just be a pity if their eyes were closed in every photo?
Demand payment in advance. Take several thousand photos and then delete all the decent ones before the "couple" looks at them. Oopsie . . . when you compel slave labor, you can't count on quality work. That would make it worth the lost day, and no lawyer could prove in court that the photographer was responsible for the wedding party and guests not being photogenic.