Something that I have found becoming a trend is that spammers (aka Mariott, etc.) make the length of their e-mail so long that the GMail App 'cuts' the content.
This is an issue because the "Unsubscribe" link is always in an additional step (e.g., you have to open another 'link' to view the full e-mail).
This is exasperated when you find that Mariott's unsubscribe link is not 'aware' of the 'subscriber' email forcing the user to input the e-mail.
With GMail's Unified Inbox, you may not have be aware which e-mail was subscribed after all and will have to re-look at the e-mail and go through the steps again.
This is definitely a dark spam method.
One of them is a local coffee roaster so I can yell at the owners face for this.
I quited gmail a long time ago, I’m not sure if you can run some custom filters on headers like LIST. Some of the worst offender uses the same sender address for both transactional and marketing emails, but sometimes the header can tell some difference.