Comments = + possibilities?

thanks for the reply

I've seen one give away where someone wrote in the description that he will re-roll if the person who won actually posted 'thanks'. I like this guys attitude, as there is nothing more meaningless than a thanks in a comment on the internet.

However I wonder if something like this is actually allowed or if that guy should/can be reported?
Next guy re-rolls if you don't post a catgif in his giveaway or whatever... legit or not?