Sometimes you get notified, sometimes you don't, sometimes you're in a test group with notification and sometimes you're in a test group without notification and sometimes it's just eBay tweaking to see reactions.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .