Not sure why you're blocked from them, last thing I saw posted here was that the list was 200++ long so don't take it personally. I mean did you ask why you're blocked?

While I admit I don't practice blocking potential buyers, (I have no one blocked) I'm sure Joe and Sarah have their reason. I suggest you shoot them an email and ask them why you were blocked so maybe you can have your privilege of buying from them restored.

Although there has been very little info given so far, it looks like the convention/show is a public event and free to enter so I wouldn't think that even though you may be on the blocked buyer list of their eBay you'd be prevented from attending the convention/event and buying from the vendors/exhibitors.