Which sources are considered authoritative, for questions asked on Seasoned Advice?
Ultimately it is up to the askers and the voters to decide if a source is reliable enough for them to accept and/or upvote an answer. As long as the answer is actually an answer (on-topic and all), we can't force people to do otherwise.
For those genuinely interested in how to personally assess the reliability of a source, first you should refer to Wikipedia's guidelines. While we are not Wikipedia and should not necessarily always follow their example, I find the Reliable Sources guidelines to be applicable almost universally.
The only notable area in which Seasoned Advice doesn't map well to the Wikipedia guidelines is on the issue of original research and primary sources. In an encyclopedia you have the liberty of simply not including any information that can't be backed up with reliable secondary sources; on a Q&A site, people will ask whatever questions they want, and we can't restrict question activity to only those questions which can be answered with such information (nor should we try).
For questions related to food or cooking, I've always used the following "hierarchy" of sources, from best to worst, as a rule of thumb:
Now, again, keep in mind that not every question on Seasoned Advice can be answered with a truly reliable source, so nothing I've said should be taken to mean that an answer with no citations deserves a downvote. My downvotes tend to be issued when a statement not only doesn't cite reliable sources but clearly conflicts with other, reliable sources.
Of course, I still might downvote an answer making questionable claims without a source - it all depends on the content, and especially how easy it is to cross-reference. The more implausible the statement, the harder it is to fact-check, the greater the likelihood of a downvote simply for not being properly sourced.
As always, much of this answer is my own personal philosophy and is not intended to dictate site policy. Different people may have different ideas about what constitutes a reliable source, and we can't tell people how to think. Nevertheless, hopefully this answer lays out some useful guidelines for others.