I never understood how it was that Korah and his crew were willing undergo a test before God to see who was right. You recall that Nadav and Avihu the sons of Aaron had taken it upon themselves to challenge Aaron’s authority and had brought their own incense to the dedication of the Tabernacle. Fire fell from heaven and consumed them. Why did not Korah fear that if he brought his incense holders into the Tabernacle the same thing might happen to him?
Similarly, they had all seen the miracles that Moses and Aaron had performed together using the staff that Moses had. Why didn’t they realize that the staff was a God given sign of Moses’s authority and expect their staffs of almond to sprout over Aaron’s?
One might argue that Korah really believed in his argument. That he was campaigning for truth and truth would out. It is true many of his supporters like Datan and Aviram or On ben Pelet were dishonest and used false and disparaging language in challenging Moses. They even refused to attend. But perhaps Korah really believed in himself regardless of them.
I incline rather to the view that all miracles are ambiguous. They are miracles if you are inclined to believe in them. But as Maimonides said, miracles are the least significant tests of God’s presence. How many miracles did they see, every day (the pillar of cloud and the pillar of fire, the manna) and on dramatic occasions, the Red Sea crossing, Mount Sinai? Yet none of these seems to have been enough or silenced the critics and the disaffected! Maybe Korah thought he was above such hocus pocus in the way Pharaoh of Egypt did?