The land records are held by a local authority who charges a taxes on the land. If the taxes aren't being paid, the land is sold at auction, and the new owner is responsible for the back taxes. Even if you don't always know exactly who is behind a given trust, you can always collect the taxes or reclaim the land. The wealth may be hidden from the Chinese government, and the local authority may not be certain who the owner actually is, but tax evasion is avoided.