I don’t know if it is true that people are selling merit for $20/each, or if they are if they are able to actually get that much. If there is truth to that, I would say it is evidence of a market that is not vibrant and inefficient. I would see that as a good thing because it shows that it is difficult to trade merit.

I am not sure what has caused this. I think most likely, it is the result of self regulation and Theymos doing a good job of selecting merit sources who will not only refrain from selling merit, but also who will send merit to posts that are deserving of merit. Those who are capable of making good posts on bitcointalk, generally will have other skills that will allow them to make money by doing things other than selling merit.