I have thoroughly investigated and tested buying upvotes from offers that were available at the time. I found that, although I received the promised upvotes, at the end of my three-week investigation, I had broken even. I earnt just enough to pay for my next upvotes each week.
Now I just post frequently, try for quality posts and hope they will be upvoted by my followers. At least that way I'm not into a mug's game. Good post :)