I would agree that there is probably no perfect solution.

I have no issue with people purchasing upvotes for their own posts, either. But I also think it would lend a certain "truth in advertising" if we call that what it is: Self-Advertising/Promotion. Same thing happens on Facebook or twitter... if you PAID to make your post more visible, there will be a line that reads "Promoted Content."

And yes, people should get more comfortable with flags... I don't have that much SP, but I do flag stuff-- specially spammy "upvote farm" comments.