PM - I do believe we have a duty to provide factual advice where possible. I reviewed my own posting on this topic to see what I was guilty of. In my case I quoted two passages from a textbook and gave full reference of the source. I also provided a link to a website run by a provider of liability insurance. I don't think there was anything improper or unethical in that.
I may have been guilty of a factual error when I joked about violating the copyright on the textbook by reproducing part of it. Another respondent said that under Canada's "fair use" exemption, I did not violate a copyright. I don't know if this is true or not.
I think I see where you are going with this, though. If a homeowner asks his neighbor, who happens to be a structural engineer (P.Eng.), about a structural aspect of his house; and the homeowner knows his neighbor is a structural engineer and/or a P. Eng., and is relying on his training; if the structural engineer provides an opinion, even though he is not being paid and there is no contract, he owes his neighbor a standard of care and is potentially liable for breach of tort (whoops, here I go again talking about legal aspects). DISCLAIMER: I AM NOT A LAWYER. THIS IS NOT LEGAL ADVICE.
So, on this website, when professional engineers provide an opinion, what is their standard of care to the anonymous party soliciting their advice? This has both an ethical and a legal consideration. Legally, can our anonymity on this website be overturned under court order and can we be held liable for advice we have provided on this website? Ethically, what is our standard of care? Given we aren't paid and are doing this on our own time, and given that conceivably every response may require several hours of research and documentation to provide a standard of care, if we hold to the traditional standard of care this website likely would shut down or would cater to non-professionals only.
Maybe it's time to talk to the website owners about getting some disclaimers added to the forums.
Good issue, PM. Sometimes I may sound a bit antagonistic, but I find your topics very interesting and certainly worthy of discussion. No hard feelings, I hope.