Frame your criticism through personal experience and specific examples rather than sweeping statements. Instead of "the food was tasteless," write "I found the soup oversalted, though my friend said she enjoyed it" - that sounds like an honest opinion rather than an insult. Avoid words like "I got poisoned," "dirt," "scammers," and other stuff that could be seen as defamation. Check that your review doesn't contain demands for money or threats - cafes react pretty aggressively to that. And yeah, even a polite review can get deleted if the owner doesn't like it - that's their right, so the actual outcome can be unpredictable.