How many people have multiple houses?

[Reinha]

This never made sense to me. If they don't want people selling houses, make the game mechanics work to prevent it.

The game mechanics already work to prevent it. Personal plot ownership cannot be transferred and plots cannot be traded. The sellers ask for a ransom and then release the plot after which it's the buyer's job to buy it from the game. The only way to stop people from circumventing the restrictions is by removing face-to-face gil trading entirely.