Slytherins have a point. There should be their flags and banner all around the fair. However, with a flick of the wand, all other banner sprout around the place as well, from the house ones, to all the other participants that might try their luck, affiliated or not. This way, everyone is represented and there are a lot of beautiful colors, banners and heraldry all around.
Oh dear. The cooks come running out of the kitchen screaming about missing ingredients. However will they make the delicious desserts?