If you have a 'year' to spare.... here's a link.
https://forums.wincustomize.com/search;ratings
Simply put, if you aren't wearing flame-retardant undies [triple nomex a minimum] threads relating to 'ratings and how/why they work' will sear your arse cheeks.
"I've heard that "master skinners" ratings are given more weight than other people. What does actually mean and what is the weight given?
Why can't the authors rate their own skins?
When one complains about drive by down ratings, how is this looked into?
I looked at "about", "privacy", "upload guidelines" and "TOS" for guidance but could find anything about ratings. Is there anything posted anywhere that helps to define rating guidelines?"
Each ranking of User has a 'weighting' to the 'strength' of their rating/opinion applied...as it matches the users' level of advancement/experience/involvement with the site and skinning. The ADVANTAGE of that is to provide more appreciation for the value of an experienced user's rating opinion over that of the casual user who often simply rates via such criterium as "I don't like dark skins so = 1 star."
Once upon a time I discovered that Admins could rate their own skins....an anomaly of user-access, long-since removed. Rating your own skin is NEVER truly subjective so is not an option.
If someone suspects Drive-by ratings and notifies an Admin said admin can view all the ratings applied to the skin...and by whom and when. That list enables access to each rater's history so time-lines etc can be reviewed. It's very uncommon, but if there may be an issue the rater in question is contacted/reviewed.
As for guidelines.....
Simple common sense. If it's really good rate it highly. If you do not believe it could be made better...rate it top rating.
If you think it's so-so rate it average.
If it blows up your computer and kills your dog...rate it low...
For more 'entertainment than poking your eye with a burning stick....follow the link at top...