Yeah, unfortunately there is no handbook to culture that anyone can point to and say they are abiding by.

I would argue there is zero wrong with enjoying or criticizing a restaurant because it's a restaurant and public criticism or acclaim comes with the business. I can also say a Japanese restaurant might be overpriced or a Mexican place salts their food too much for my liking. Or even that I prefer to avoid all Chinese food because it sits heavy in my stomach. All okay because it's all relative to me: "I don't like this", rather than absolute: "This is bad and a poor representation of True X Food."

Then there's the grey area where a white person who has never been to Iran opening up a Kabob joint because they love the food and it's good business. As an also-half-persian, I have no problem with this, but would probably say the politically correct thing to do would be to call it "Kabobs" and not "Persian cuisine". In the former case, you are saying: "I am making this food" rather than "I am representing this culture".

Annoyingly, this is a subject where the stakes are unbalanced and if you're right, it's no harm done, and if you're wrong, you're a grade-A asshole. I have the feeling social liberalism and political correctness will eventually settle on a consistent set of rules. But for now, yeah, degrees, possession, and respect.