I was very patient with one client (who'd been referred by an excellent client) who turned out to be a mess.  He was polite for a while, pretended he wasn't sure what he'd worked out with us for a payment policy, 

He was nice at first, then pretended he didn't know what our payment arrangements were,  then ignored me, then after a number of professionally worded emails from me eventually stating my next steps (which would include posting on industry websites - I also said I'd be happy to post positively when he paid) and other means which would NOT include a collections agency, HE screamed at me in all caps, said some off-color things and he actually told me he was going to sue US for libel & was going to report me to the authorities for extortion.  I still laugh at that last part.

I told him he was welcome to proceed and I'd be happy to provide all the emails and invoices as supporting docs.  At the same time I told him I'd be filing a complaint with his local Bar Association (giving him pertinent info so he was aware I knew who to contact).  A check was FedEx'd the next day and he had the gall to email me, Mr. Friendly now,  to ask me if it was received and would i remove the posts.  Good to my word, I posted he paid but gosh darnit, can't remove the posts, sorry.