Sigh. Money rules everything, doesn't it?
The government could pass a law making all meteors falling in the country government property. The practical effect would be to prevent these auctions from happening as well as a prosecution mechanism for when someone is caught trying to sell. The black market would still exist, but finding buyers willing to pay as much as auction events would be more difficult.
Because meteor rocks are a scarce resource, they should ideally belong to scientific organizations, not in people's private collections.