eBay has recently removed the option for 14 day returns on the US site. We will have an update soon that should remove the option from our lister as well. I believe this is what you received that warning for.
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 .