I think there are two ways to achieve this: You can either tie the name to enough value that registering many names isn’t profitable (that’s why names have at cost at all, otherwise I’d be able to register every available name for nothing), or you can check some attributes a user gave himself. These are e.g. social proofs for Github, Twitter, Facebook and so on.
You can’t eliminate the chance completely, but you can try your best to do so.
For some decisions people vote on, the normal price of a name might not be enough to stop people from voting with multiple names, so you could increase the value behind it with letting users burn a certain amount. In some other cases, you could specify a list of names which are allowed to vote (e.g. you like to vote on your companies 5-year plan).