http://Auctionsniper.com is around 2x bigger than any of it's competitors and has the most features and highest reliability. They also own and managed their servers. Very few others do. That leaves your info on shared servers managed by 3rd parties and not the companies doing the snipes.
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 .