Hi.
I enable feature to use rating for placemarks. Just set way to call in map details, on Advanced options tab, field Placemark Rating
The main thing of how I check do you already vote
– if you didn’t connect – I check by IP + HOST + placemark ID
– if you connected – I check by User + placemark ID
And if I found record of vote, I show message “You have already voted”
My rating system differs from common case.
In common examples rating and count votes stored in fields of object (placemark), and just correct when created new vote.
I store all votes and calculate by it when new one vote and after that update summary field.
Ie if you update field, then when new vote comes, it will be recalculated on all votes again.