1) Real Estate mini-sites 2) Designers submitting their clients
I'm not a directory owner but if I was here's what I'd do...
If the listings are their own (i.e. not a feed from another site) and you break down your real estate listings by city also then I'd approve.
If the sites are quality and not all built to a set template then I'd approve. The common theme might be the fact that they all were done by the same person/firm, but if they're worth listing then that shouldn't matter to you or Google.
1) Real Estate mini-sites
2) Designers submitting their clients