I'd like to make it known that there are ways to decrease the chance of this happening, without restricting the vote to purchased users.
- Blocking TOR users from voting (TOR provides a list that can be used to do this)
- Blocking known proxy servers, there are comprehensive blacklists of proxy IPs available to block an account
- Blocking throwaway emails
- Requiring minimum register time
- Requiring minimum post count
- Requiring minimum forum registration
We could also do it by having a point threshold, a user would have to meet X number of points to be able to vote. I'll give an example.
Number of points to vote: 10
30 points: Purchase Game
3 points: Registration date longer than X amount of days
Base point of 6 points: Meet minimum post count to get 6 points and 1 more point is awarded every time they meet X more number of posts
1 point: Uploaded avatar
1 point: Signature set
-10 points: TOR/Proxy IP
-10 points: Throwaway email
-10 points: Forum ban
Add other positive and negative factors to decide whether the person is elligible for vote, the more comprehensive the system is, the better.