I would say a large portion of reviews on most online sites are bogus in one way or another. It's a world wide web of lies.

Here are some examples of things I've seen first hand. Managers making multiple fake accounts to post reviews with (some even pull the long con and keep the accounts reviewing other businesses for years so it's not a one review account). Bribes to customers for 5 star reviews. Rival companies leaving 1 star reviews on all competitors. Disgruntled employees leaving fake reviews as revenge. Customers using a bad review as a threat to get what they want. Websites offering to make bad reviews go away for a fee. And much more.

And it's been going on for longer than the internet. I worked at a store once that got hammered on the local news after a customer called the station to complain they were not allowed to return a product. But they left out that the return was denied because that person was cut off after buying and returning several thousand dollars worth of products every month. And the BBB has been selling accreditation to businesses for over a century while convincing consumers that it actually means something.