[marcus_holmes]

Australian English has this... "yeah, nah" and "nah, yeah" are commonly used as replies to negative sentences. Well, all sentences really, but in this context negative ones.

"You've got no chance of beating that thing in a fight, mate" "yeah, nah" (I agree)

"Reckon it's never going to rain again?" "nah, yeah" (it will, eventually)

[nicwilson]

and the classic negatory chain of Yeah! (yes)-> Yeah, nah! (no)-> Yeah, nah, for sure! (yes)

[mocha_nate]

Pretty sure you can mix and match and it depends on the emphasis and tone of the speaker:

“Do you serve Pepsi here?”

-(no) “yeah no, we are all out”

-(no) “no, yeah we are all out”

-(yes) “no yeah, we got it”

-(yes) “yeah, no we got it”

[marcus_holmes]

it's always the last value that counts.

Your example of "no, yeah we're all out" doesn't actually work, because the "yeah" is dangling. The "yeah, no" works (the yeah agrees with the question, we do serve Pepsi, but the no modifies it because we're all out).

and the same for the "yeah, no" in the second example - the "no" is dangling.

but yeah, it can be confusing if the tone of the original question implies a negative (like "you don't serve Pepsi here do you?").

took me ages to work out that the first value doesn't matter ;)