(1) What should I do when someone refuses to provide evidence to substantiate their statements, which I believe are incorrect?
(2) How should I respond when they tell me to take their word for it because they are a native speaker, even after I provided authoritative evidence that contradicts their statements?
I don't know how to deal with such situations. I mean no harm or disrespect to anyone.
In the meta post Submitting Answers that merely answer the question, J.R. mentions
... it's important that answers be accurate. Before you submit your answer, look at it with a critical eye, and ask yourself, "How would an O.P. (or anyone else visiting the site) know that my answer is correct? Are they just supposed to take my word for it?"
Note: I'm a native speaker; therefore, I know what I am talking about does not qualify as proof of correctness.
Sometimes, I see answerers make strong assertions without providing sufficient justification (e.g., "no one ever says this", or "we never say this").
When I feel that something isn't quite right, and that I can't agree with their claim, I ask them for a reliable/authoritative source (e.g., anything from google news, google books, usage examples, ELL/ELU posts, Wikipedia, English Language Forums, Blogs, and Dictionaries).
I have a few reasons for this: (1) if they are able to provide an authoritative source, then it helps me learn something new; (2) an authoritative source is always helpful for the OP as well as for other users in the community; and (3) it allows me to trust this user. J.R. talks about this in their answer to the this Meta post: Cite your sources!.
I recently answered a question: "What is the “small window” on a web page called?"
I wrote, "It's called a drop-down menu". I provided a definition from Cambridge Dictionary, a Wikipedia link that shows my answer is one among other options, and an Ngram that provides a usage comparison. I also pointed out that "drop-down list" is more commonly used than my original version as per the Ngram.
An answerer answered (I added the bold emphasis below)
It is NOT called a "drop-down menu". While that term might be "technically correct", sort-of, because it is a menu, and it is drop-down, no one will ever say "drop-down menu", because they will say "drop-down box".
I had to comment because their answer was directly contradicting my answer. I wanted to know if they had any sources to substantiate their claim.
Me: Do you have any source that can substantiate this claim? "...no one will ever say..." really? Did you check google books before you made this statement?
Answerer: Yes, I speak English natively and have spoken to other Americans during my life before, who have in several cases referred to this item on a computer screen. I have also read articles in English before. If all of these thinhs are true, then each English user will know that my statement is correct.*
*This is essentially Gaslighting (57), The Identity fallacy (64), Red Herring (106), or Anecdotal evidence.
What just happened? I did not ask the answerer if they were native or non-native. I wanted to see some sources to cross-check both answers (I had already provided credible sources to support my answer; show me proof that the sources I provided are wrong).
I will always trust native and non-native speakers who have established themselves here and in ELU. The quality of their answers speaks volumes. But sometimes (very rarely though) I find users I can't trust.
Me: "... saying it like that sounds like you're ordering someone to get you chocolate quite rudely." Do you have any source (e.g., dictionary entry, articles, etc) to substantiate that claim?
Me:"No one says it like that in real life." - Interesting. Any sources to support this?
Answerer: As a native speaker, that's how I often hear and see English used. "no one says that in real life" is just based on years of experience and using English. "that sounds like you're ordering someone rudely" is because when someone says it like that, that's just what usually it means.
I wanted to know how "I want a chocolate now" could only "[sound] like you're ordering someone to get you chocolate quite rudely."
Also, I felt "No one says it like that in real life" was too strong of a statement for "I play games now". That would depend on the context (e.g., I can imagine a professional gamer saying "I quit my job. I play games now - full time! I compete in tournaments - the money is great!). Surely then, it can be said informally in speech. Had the answerer said "It's not common usage" or "It's very informal", I would have no problem.