The courts, if he gets sued for libel. He's put up enough to merit a case against him, if it what he is saying is false. It doesn't appear to be, but you never know who you are "up against".
The proper course of action, when things get into legal territories, is to remove the online posts, or to make a single post explaining the situation in some detail and then stopping. Devolving into name calling is just bad. Exposing name, address, and phone numbers is very bad, especially if it is to a private residence instead of a place of business. That, IMO, crossed into libel territory.
If I were graciocues' attorney, I would tell him to put a sock in it and clean it up before it derails further. That would include a deletion of this thread and all sub-forums he posted in. His anger and venting has likely taken him into territories he does not want to be in. In all likelihood he will not be able to afford an attorney to defend him when the time comes.
Discussing legal situations, or a course of action, is one thing, naming persons and labeling them is another. If you publish on your blog (azbilliards.com in this case), you had better be 100% solid.
Lookup the online defamation law.
Yep, pretty much this. Sometimes you can get away with saying "so and so is a thief," as there are no specifics. But when you say "so and so stole this exact cue," you get into some bad places if you're not careful. You have made a specific accusation, in which if false, can hinder someone's reputation. In this case if the guy in question buys and sells cues, it can directly hurt his reputation selling cues.
In this situation, where even if he isn't doing the "right" thing by returning the cue, he may in fact be doing the "legal" thing. If that is in fact true, publicly claiming he stole the cue, is a very, very bad idea.