Tankbuilder, in a perfect world, such problems you opined would not come about. But in practical terms, such scenarios will still rarely happen in reality. Consider this: the usual standard is to have three judges. Why? In case of an absolute tie of opinions, it offers a chance for a tie-breaker. Also, this means more experience & improved 'observation' (more eyes), yes? So even if you are judging models you've never built yourself, the others on the team can help you understand what you're dealing with & guide you. After all, you are a modeler and understand the process. It is a matter of looking at the work before you and applying first the basic standard; after that, where direct experience comes into play, the others can help bolster your 'ignorance'.
Shows have a progression that supports the judging population, as well. Smaller shows, where the judges have less experience, are fewer in number and have more possibility for conflicts of interest - they also have lesser numbers of entries, the overall skill standard may be lower and hence the judging more 'obvious'. Often the best models will be quickly culled from the pack so the focus falls to just the few. Even then, minor (instead of major) construction issues may determine the outcome without ever reaching the level of 'splitting frog's hairs' over accuracy, difficulty or refined skill.
Larger shows, conversely, will have more entries, more candidates for judging with higher levels of experience. Again, the balance is achieved that helps keep the 'noob' from creating havoc. The only risk is where an entire team are neophytes to a category they are judging AND the models are of such high standard that discrimination is only possible if you are a SME (subject matter expert.) What then? Then the coordinating judging will be called to 'step in' and officiate or make adjustments to the team. So, the checks and balances will take care of the problems - as long as judges are honest about their abilities.
Case in point, I myself judged figures for the first time at the 2014 Nationals (with the consequent high standard of modeling to boot.) I was an OJT (on-the-job-trainee) judge, but my opinion was listened to being a modeler and having judged before. Even with these beautiful figures, where painting technique apparently reins supreme, the basics still mattered - to a point. I learned quite a bit about figure modeler's expectations by this experience - and know it isn't the same as say, aircraft or armor modeling. I also joined in with some Diorama judging which also had a different subjective emphasis (and rightly so...)
If there was anything that I felt truly needs to be addressed, it is the issue of model placement in categories. To illustrate, consider an aircraft model that is largely scratchbuilt. In fact, it would meet the criteria for the scratchbuilt category. However, being an aircraft subject, does this not also mean it can be entered in the 'regular' aircraft category? I believe that decision should be left to the modeler, not a judge. If something meets the criteria for a category, then it should be left there and not moved *just because it could also fit another category.*
This issue became apparent to me when several armor-type vehicles, affixed to 'natural landscape' bases with several figures (but consistent with vehicle crews) were relocated to the diorama categories. These models did not 'place' in any fashion because they didn't illustrate any prerequisite 'story' that a diorama is supposed to "tell". They were merely vehicles with crew figures and, as per the rules, met the criteria for the 'vehicle' categories - where they were originally were placed by the modeler. Yet a judge some how determined they belonged elsewhere solely based on what they deemed was excessive groundwork or figures. What was missing was the 'story telling' aspect of a true diorama entry. To rationalize this one judge actually stated 'well, it just has to have a 'story line' doesn't mean it has to be a good one' or words to that effect.
To me, this is wrong and frankly, arrogant. So what if a model has an intricate base or figures around it in a 'vehicle' category? That just means those elements are to be ignored for judging. Such things would be considered only if entered in a 'vignette' or 'diorama' category - otherwise, they mean nothing. Criteria for categories should be objective and not subjective. Otherwise, we have happening what did happen: a hatching baby dinosaur was NOT in a diorama category - but why not? Certainly, there was more 'story' to that subject than a single crewman smoking a cigarette next to a jeep - which *was* moved into the diorama category. I say, if a subject meets the criteria of a category then it should remain in that category in spite of any other elements that may be present. I say a large scale rider astride a military motorcycle could be in Figures, or with military motorcycles/ vehicles (under the correct scale) OR in with the other automotive motorcycles. Let the modeler decide which of the possible, and correct, categories to compete with the knowledge that the category will determine how it will be judged. Doing as we have been doing just makes things harder and more contentious. Why should the builder's decision be subject to second-guessing? The criteria aren't that complex or general that they are open to interpretation, after all - except for things that make them that way unnecessarily.
That should be addressed, and soon.