KenM said:
Banning someone after the fact won't work - they've already accomplished their goals: get free prints without doing any work.
I therefore agree with limiting this to subscribers.
I don't know if people are trying to get free prints. My purpose for joining an exchange is to share my work. I want to make someone smile when they look in the mailbox and have a package. I'd like to think that they would have fulfilled their obligation as well, but at least I know that I did my best.
Wow, I should be a motivational speaker.
Back to the subject, I voted YES.