Well there isn't really any way to tell who is or isn't returning the votes. Say I visit 10 threads and vote for the posters as well as post my link as a reply in each thread. If I get only a few votes afterward, I have no way of knowing which of those 10 posters were the ones who returned votes.
My particular case is made more difficult by the fact that mine requires registration on the site. I realize that people do not wish to be inconvenienced by this, but should that matter?
I found another forum similar to this one that had separate sections for easy or 1 click voting and "complex" voting, which required registration, email validation, or more than 2 steps to complete. Perhaps this forum could do something like that.
I think it would be a good idea to have a section for the more complex voting. Thing is, let's say someone posts a thread asking people to simply Like a facebook page. Then, while it isn't likely, it would be possible for several people to reply to that, Liking their page and then asking them to return a vote on things that all require emails or registrations. The amount of "effort" exchanged in such a case would seem to be very unbalanced.
If, then, there was a section of the forum devoted to those who wanted votes on sites that required more work, such as registration, then it would be naturally expected that the exchanges would be more fairly balanced.