If you don't specify I can't help. If marketing = 3rd party then you can block these using the hosts file at the domain level, which I do. This blocks >95% of crap cookies. A clear question gets a clear answer.
You're right of course but 3rd party seem to be the great majority, so blocking them is a big easy win. Also, only 3rd party cookies can track between domains/sites, so that stops that, or so I believe.
The only entity that can specify whether a cookie is marketing-related or not is the website. No one else can.