[tylermauthe]

It's not libel if it's true! But it may be some sort of fraud / infringement.

[dangrossman]

Debt collection laws make it illegal to inform anyone about a third party's debt (except their attorney, creditor, a credit reporting agency, and their spouse). It's not libel, but publicly posting someone's debts is still illegal.

[gte910h]

Are you sure that applies for businesses? Most laws for consumer protection are personal, not business level.

[jiggy2011]

Assuming the guy hasn't been paid then whatever contract they had is probably void anyway.