While it's within the rules to allow two or more people to open branches of the same brand/store, or one person using alts, given the scarcity of the commercial spaces now and in the foreseeable future, I believe it would be more fair to merchants to restrict ownership of more than one space until every merchant who wants a space has one.
There have been a lot of complaints about "fairness" and "rules" on the forum, and even more discussions (and disagreements) about what a store is or what sales/commerce mean, but this is fundamentally a blatant example of pure greed, a person not having any sense of empathy or consideration for other merchants by claiming two spaces for one store.
While this is a qualitative call, it only seems like the right thing to do, although given how cut-throat it has been to grab commercial spaces (I've see 14 avatars all trying to scoop one abandoned store) and their on-going scarcity, something needs to be done to assure users that LL is playing fair and allowing everyone to get s spot at the start.