In Thailand it is considered defamation to say something about a business or person that harms them, EVEN IF IT IS TRUE.
If, for example, you say that the prices are too expensive, and that takes away customers from the business, it will be defamation even if you can prove with the invoice that it is true.
Since in the first world defamation is only considered if it is a lie, many Westerners fall into the trap of leaving unfavorable opinions on Tripadvisor or Google Maps about restaurants or hotels, without thinking that in Thailand this is defamation, which carries strong fines and jail terms.