I have also noticed soem strange votes in the past.
The way this kind of problems is handled on another site is :
To vote the account has to be older than 3 months and have a minimum of 10 posts.
A stronger requirement could be :
To vote the account has to be older than 3 months and have posted at least 1 original work.

Of course in these matters there is no absolute protection against "fake" accounts but similar measures reduce it to a minimum.