Can I get in trouble for a bad Google review?

For most people the answer is no. A bad review of a business you actually used, saying what happened and what you thought of it, is what reviews are for, and the law protects it. Under the Defamation Act 2013, honest opinion is a defence where the review is clearly an opinion, shows what it is based on, and an honest person could hold that view on the facts.

The line that matters is between opinion and false fact. "The tiling was poor and I wouldn't use them again" is opinion. "They took a deposit and never turned up" is a statement of fact, and if it isn't true it can be defamatory. Truth is a full defence, so a factual claim you can back up with messages, photos or bank records is safe to make.

Businesses face a high bar before they can sue. In England and Wales a statement is only defamatory if it has caused or is likely to cause serious harm, and for a company that trades for profit that means serious financial loss. Scotland has its own law, the Defamation and Malicious Publication (Scotland) Act 2021, with a similar test. A claim generally has to be brought within one year.

People do get into trouble with reviews that aren't really reviews. Posting about a business you never used, a competitor posting fake negative reviews, or a coordinated run of reviews meant to damage rather than inform can break Google's policies and, where it is done in the course of business, the UK ban on fake reviews. Sustained targeting of a person can also amount to harassment.

From the owner's side, the same rules apply in reverse. A one-star review you think is unfair is almost always honest opinion, and a legal letter tends to draw more attention to it. If a review states specific false facts that are costing you work, speak to a solicitor about your case. This answer is general information, not legal advice.