That's fair.. I wasn't the original poster (nor was I offended by the request - see below for my own self-reflection), but I see your point for sure.
I'll admit that I can be guilty of speaking from personal authority/experience in forums and not feeling the need to provide references, because it's just a forum on the Internet and there's a limit to the effort I'm going to put into a discussion with strangers, but the other side of that is valid and there's nothing wrong with asking for receipts if you're skeptical...
In the end I am realizing I mostly took exception to the tone of the other person (not the demand itself), and that's on me.. I should have just ignored him and moved on. Not everyone knows how to communicate properly.. Even now he's responding to my other comments (and even jumped into this thread) to antagonize further.. oh well.