關於Hamburgers的意思和用法的提問

A: × Hamburgers are regarded as first foods, but it doesn't mean that they are always cheap.
✓ Hamburgers are regarded as fast food, but that doesn't mean that they are always cheap.

A: This actually changes the meaning to be the opposite meaning.

"are not always fail" = they are sometimes fail, but not always. Sometimes they are win instead.

"are always not fail" = they are always win, they are never fail.

---

or to use another example of how this phrasing works:

"are not always bad" = they are sometimes bad, but not always bad. So sometimes they are good instead.

"are always not bad" = they are always good, they are never bad.

----------------

Although saying that "[something] is fail" or "[something] is win" is pretty slang. If you need to say this in a more standard way, then saying it is lame or terrible instead of "fail". Or good/great/wonderful instead of "win".

So:
Hamburgers are always lame. (not cool, not impressive)
Hamburgers are always terrible. (never a good option, don't like them)
Hamburgers are always great. (always good, always a good option)
Hamburgers are always wonderful. (always good, love to eat them)

A: Hamburgers are regarded as the representative of American junk foods, but seem not to contain anything (particularly?) bad, while french fries and cola are terribly bad for our bodies.

Because you are discussing symbols of fast food, I changed the generic "fried potatoes" to "French fries" - the specific variety of fried potatoes that many people eat with hamburgers.

A: × Hamburgers that was served at authentic restaurants are good but quite expensive.
✓ Hamburgers that are served at authentic restaurants are good, but quite expensive.

A: Sounds great!