Google does indeed look at the other sites a webmaster or business owner operates when one of their sites gets a manual action - at least, some of the times they do.
It seems like Marie Haynes is dealing with one spammy client and when she posted on Twitter asking for Google's Matt Cutts to help, he did chime in. He talked to her about all the spam this site did on the site in question and on other properties.
He points out how Google may have noticed they have multiple spammy sites:
He goes on to imply Google is aware of "several."
@Marie_Haynes and make sure to press your client about exactly how many "quick case" sites they own, because it appears to be several.— Matt Cutts (@mattcutts) March 7, 2014
This all builds a bad feeling in the Google webmaster analyst who is reviewing the site:
@Marie_Haynes so I worry that you haven't truly gotten through to your client, who shows signs of long-standing, mass, deliberate spam :(— Matt Cutts (@mattcutts) March 7, 2014
So while Google may not always take the time to review other sites this webmaster may operate, when they do, it can lead to a mess - if you've done sketchy things across those properties. And it seems this specific business owner dug himself deep into a hole.
Forum discussion at Twitter.