Hello Mikez,
Well about cheating if some user get suspicious, you should check his user details page:
Example -
http://visiolist.com/demo/details/visio/
You can see his daily votes, monthly etc... and if votes are incraised by high number that means he cheat.
If some day he gets regularly 30 votes, and next day 300 or 500.
Maybe there are other ways, if there are any please share guys