Hi @KaKaRoT,
By default, all leads/contacts from SFDC will be marked as marketing contact in HS.
But you can mark a few contacts as non-marketing contacts Manually or via Workflow. Please go through this article to learn about the steps needed to mark contacts as non-marketing contacts.
Best practice:
1. Create an active list of contacts whom you want to mark as non-marketing contacts
2. Set up a contact-based workflow and put the “Active list” created in the above step as a trigger then follow the steps given in the above article.
For more queries reply to this thread.
Thank you 