*sigh*
The simple question is accusatory, sir. Your phrasing is either poor or rude.
"Has anyone actually met with this guy?"
This sentence implies that there's not only doubt of the poster, but that said poster could be up to something, whether nefarious or not.
"Can we affirm that this is safe?"
This sentence pits "us" versus him. Very few of the tens of thousands of people here, not to mention the potential thousands more encountered every year (assuming major metropolitan locale), can be accurately affirmed as "safe". Nevermind the generality of "safe" in such limited context
If you wish to appear neither accusatory or poorly-worded, it would be better to consider how you post a question to someone else's post. That will be true in discussion areas as well.
My response in no way should be interprets to infer that I know him, or can validate. I speak to base courtesy.