I would like to throw out ideas for candidate trees
tree that have way too many branches (big box store nursery stock or over grown trees on your property)
trees that have no branches (such as cutting a big tree down to a branchless stump)
Air layers
"yamadori" something grown in the ground that is not on your property (or at least the part of your property you maintain)
A few other potential rules:
Maybe not allow trees that are already in a bonsai pot unless it is without branches?
A broad view picture of where the tree is growing, with the tree in the pic, before harvest for competition, unless it is an air layer. (this is it in the big box store or this is the forest I am about to dig it out of etc) receipts are good too?
Maybe a part of the the points can go to how the tree was acquired? Best story gets a point or something? The person that climbs a thirty foot crabapple for an air layer gets a foot up on the person that buys a Lowes juniper.
I'm just trying to think of ways to keep everyone on an even playing field and keeps it fun for participants and watchers alike.