Simply not displaying who rated you up or down (just like on here) is the first step towards that.

That is definitely something that has been a consideration since day one though. Epinioins was widely disqualified as a reputable source because people formed such "cartels" to take advantage of their paid review model.

But still people can open multiple accounts or ask their friends to log in and hike up the karma? They can manipulate the reviews and swing it in their favour