I worked out a method to build a bot network to game reddit with. I have not implemented this, so I can't be sure what the results would be.
You want to build up an arsenal of accounts that have a good amount of karma so they don't look like bot accounts. You also want to route them through various proxies to hide their true IP origin.
Starts off with some manual work to get the accounts set up, but you could also use a service like death by captcha to get around bot checks and automate account generation and karma building.
To build up the account karma, automate the process of reposting top posts from 3 or more years ago. You don't even need to change the title, the suckers on this site will still upvote it, and you'll probably have some people calling it out in the comments but it doesn't even matter.
I suspect this practice is already in use because I see it pointed out quite a bit.
You can work the accounts together to get the comment karma built up on them. Use the others to post the top scoring comments from the reposts. Reddit will predictably upvote the comment.
You can repeat this many times, and within a short time you could have thousands of accounts at your disposal with karma in the 1000's.
You also want the accounts to appear as human as possible. So they'll need to browse and vote on things randomly and at certain hours of the day, not around the clock.
So, each bot will be a node operating through a proxy on its own IP that will run the human behavior patterns while they're idle.
They will all refer to a centralized directive controller that will command them to vote on certain things, which they will do at a well spaced interval, not all at once, to avoid detection. But within an hour or 2 your thousands of bots should cast their votes and you could cause the vote direction of any post or comment to sway significantly.
The only thing you really need to set up a vast network like this is resources, and time.
I imagine someone with sufficient motivation and money could pull this off.
You will need a centralized