Hi Andrew,
The main risk you would run into is a defamation action, however the Defamation Act (WA) introduced a general rule that corporations cannot sue in defamation, unless they can bring themselves within the definition of an “excluded corporation” - which is either a non profit corporation or it employs fewer than 10 persons and is not related to another corporation. Therefore if the company you wish to spout about is a small company or its not for profit, I would tread carefully. There are also defences to actions for defamation such as truth and public interest, which may still get you off the hook.
There are other actions that may still be brought by companies, such as injurious falsehood however this involves a situation where a defendant maliciously publishes false material which causes special damage to the company or its property. As long as you are not being malicious and publishing or stating facts regarding poor service or products then you should be in the clear.