There's no central standard for how RWA contests are conducted. Each chapter sponsoring a contest comes up with its own scoresheet, recruits judges according to its own standards, etc. (You might think a contest draws its judges primarily from the sponsoring chapter, but that's not always the case. They almost always have to recruit from other chapters. I'm a fairly ordinary unpublished RWA member--I'm a member of the "Pro" program and have finaled in a couple of contests, but that's it--and I probably judge 6 contests per year, only one of which is sponsored by a chapter I'm part of. And I could judge more often, but what with having a full-time job, a husband, and a 2-year-old, I'm trying to stop saying, "Sure, I can do that! Happy to help," EVERY SINGLE TIME a call for volunteers goes out.)
Anyway, though there's no set standard, chapters DO share information, and so there are a few common scoring systems. Most contests use a hyper-detailed scoresheet, with several pages of detailed questions on Pacing, Point of View, Conflict, Characterization, etc. As a judge, you score each question, usually on a scale of one to five, with a perfect score somewhere in the 200-300 range. A few ask you to score on the broad areas above, but leave the judge more discretion to define what constitutes good pacing, appropriate conflict, etc. And one or two use the Golden Heart scoring system where you simply rate the entry on a scale of one to nine, but unlike the GH ask you to provide feedback explaining your score.
As a judge, I prefer contests that use the less detailed scoresheets, such as the Molly, the Royal Ascot, and Romancing the Tome. I often feel the hyper-detailed scoresheets cramp my style and force me to major in the minors. E.g. occasionally I'll see an entry with some glaring flaw that ruins the reading experience for me. If the scoresheet doesn't address that flaw, or only gives it one five-point question on the 250-point scoresheet, there's no good way for me to score the manuscript as I believe it deserves. And on the other side, I've read fabulous entries that just don't quite mesh with that contest's scoring criteria--i.e. an entry where the hero and heroine don't meet in the first chapter, but the scoresheet devotes a lot of space to hero/heroine interaction, sexual tension, etc.
So, if you're entering a contest, always, ALWAYS look at the scoresheet before you mail in your entry. Most contests post them to their website, but if it's not there, you can always email the coordinator to ask. If your goal is to final and get your manuscript in front of an editor or agent, stay away from contests where you KNOW you'll be giving up points because of the nature of the story. Of course, you're always at the mercy of the judges. Some of the lowest scores I've ever received came from a contest where I thought the scoresheet was tailor-made to play to my strengths. But my judges didn't connect with the story and scored me accordingly. And of my two contest finals, one came from a hyper-detailed scoresheet, the other from a contest that uses the GH system. But as much as these things cost to enter, it makes sense to target your entries where you have the best chance of success.