Interesting... I was unaware of this but I'm not surprised it's happening.

I imagine though, that if buying upvotes became a wide spread approach, that a market would develop around the price of upvotes. At first glance, my guess is that the price of an upvote would probably end up being greater than the amount that upvote would payout, since buying an upvote is not just buying a portion of the rewards pool.. but also attention. I imagine that the seller would be able to sell upvotes for significantly more than they would get from self-voting

So my guess is that people would end up buying upvotes at a financial loss. So then buying upvotes would become a method of promotion. This would mean that people would only buy upvotes for content that they considered worthy of promotion... hoping to see a return on their investment based on the attention they purchased.