Each modeler must determine on their own which level of "skill" they have executed on that particular build and in general for their skill set. Things that could, but not universally, elevate a build into the Advanced category would be things like using PE, scratch-building, advanced or complex paint/finish/weathering techniques, resin conversions, etc. although an OOB build can certainly be considered Advanced as well based on how it's finished.
Ultimately it's a subjective classification...and those entering the contest for the first time are encouraged to look at past month's contests (and winners) to get an idea of what the competition tends to be like in the different categories and place their entry in the appropriate group according to their comfort level. Generally speaking, the entrants over the past months where we've had this breakdown in place have done a good job of sorting themselves into the right category. Some will stretch from the Intermediate to the Advanced, others will be more conservative in the opposite direction, but it ultimately balances out in the end.
Since the photos are the model and, unlike a standard contest, we don't have the actual entry in front of us to evaluate, the modeler's choice of category is respected. The higher level prizes go to the Advanced category as a further incentive to prevent people from "under valuing" their entry to increase their chances at winning but beyond that, it's up to the builder to know and decide which level they should be competing in.
(and sheep among the wolves)
