I think your comment hits it on the head. Most contractors complained about HO's, not necessarily businesses.
There are two things: (1) YOU run a business and for the most part have a business identity, (2) HO's are individuals and are consumers of your products.
Bad mouthing (whether what you say is true or not) a company or entity is one thing, bad mouthing an individual is another. You can sue for slander and libel (mostly libel) if someone spreads via the media, untrue rumors and damaging text about your business that has no facts or truths behind it. However it will cost you a ton of money and you have to show actual monetary loss due to the actions of that individual(or other business).
But if you as a business go after someone (an individual) in the media (which includes the internet) for being a "nasty person", or for not paying their bills, or whatever, then the court (both legal and that of public opinion) tends to side with the individual rather than you as a business.........why??? cus it's part of "doing business", and, it can be assumed that if you run a business, you are supposed to be able to handle difficult clients and those that don't pay.
There are retailers that post the checks of people that have bounced their checks .....that's ok. The person has actually committed a crime by bouncing a check. But a person that, for instance, doesn't pay you, can only be found guilty in a court of law and a judge or jury must decide their guilt (i.e. not you). This is the old "charged" but not convicted thing.
So, let's say that someone, like an HO, violates their legal contract with you.....for whatever reason. Being a nasty, PIB type person, or, having bad behavior, is not usually considered a breach of contract. So the contract is broken and you now have to head to court to get a judgement. If the judgement is in your favor, those judgements are now public. So you can be justified and legally able to post the judgement on your website, or, direct people to the legal postings. Since judgements are public documents you can get away with it.
I am not a lawyer, but if you post something without legal precedent (ie: judgement or ruling), then it's your opinion vs theirs. And all they have to do to prove damages is to have one contractor not do work due to your comments, or, show any kind of damages (psychological, employment, credit, etc) if one of their friends or employers sees your comments.