You need to do it with user accounts so the search engine team can remove fake clicks and ban the user. Users with a low amount of ratings won't have any say in

You need to do it with user accounts so the search engine team can remove fake clicks and ban the user. Users with a low amount of ratings won't have any say in the rating of the site, since they will have a low confidence. They will first need to rate a few hundred sites (valid ratings, because if they don't have high validity with the rest of the sites in the database the confidence this is a valid user will be low) to give the spam site a high rating. So they will have already built a database of good ratings before they can give the last vote that they get paid for? Also, you can manually remove a spam site that uses this tactic and all their money will have been wasted.