Every single online review platform can be gamed by just soliciting reviews from people who have just had a positive experience and shunting people who have just had a negative experience to some kind of alternative channel where their complaints can be hidden from the public and/or resolved.
The more aggressive the company is in managing public perception through online review platforms, the more challenging it will be for anything negative to get out there.
Companies have a strong incentive to systematically manipulate online review systems. The people leaving the reviews 'organically' just have some intrinsic motivation to write them. Over time the shills will win no matter what kind of rules you set up to prevent it. To some extent also the capacity to run a good shill program is a signal of the health of the business doing the shilling, so it doesn't completely destroy the value of them.
The main way to counteract this kind of shilling is for objective and trusted third parties to compare companies, products, etc. with tests that cannot be faked and perhaps combined with some subjective evaluation. If the user is not paying to maintain the accuracy and objectivity of the reviews that they're using to inform their decision, then why should they expect it to be anything other than some combination of shill-spam, the odd lunatic, and the increasingly rare fair-minded and well-informed reviewer? The aggregate of all those things is not necessarily the ideal wisdom-of-crowds outcome because all of the inputs can be defrauded or otherwise manipulated in various directions.