Hi Graham,
Here are a few insights that hopefully help you out:
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The site could be penalized individually or as a hub depending on the severity of the duplicate content.
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Use a tool like Penguin Tool from Baracude Digital to check for penalty.
http://www.barracuda-digital.co.uk/panguin-tool/ -
Real estate is notorious for duplicate content. If you are doing SEO for a real estate website, your first move should be to restrict access to the listings and then try to identify other types of content you can use to rank. Also, remove as much boilerplate as possible and find something unique, at least a couple of sentences, to write about your listings. Add unique content to pages where duplicate content exists. Add entirely new pages and frequent blog posts rich in original content.