I report people I sell selling houses. That's really the only thing you can do. Other than that, until SE fixes housing in general, you'll have to stalk the residential areas. I caution anyone giving in to the real estate barons. I really do; it's extremely unfair for them to ask for large amount of money to relinquish land.

As far as having multiple houses, I see no problem with each toon owning a house. It's not like alts can share, and for RP reasons, some toons might like to live in one district as opposed to another who prefers a different one. There are many reasons why people have multiple houses. I don't want to see people penalized for it.