If a friend asks I usually accomodate but friends seldom ask.
If a stranger asks I politely decline.
If a cop asks I comply.
Very well stated. I wouldn't hand my gun over to someone whose experience and intent I'm not familiar with. If they really want to see it, I tell them that they can bring some ammo to the range sometime and I'll let them see it and shoot it in a controlled environment; at which time, I'll be carrying something different.
It amazes me how willing some people are to hand over their gun. My son and I were at a small, rural general store recently where a guy was carrying open. I have seen the guy quite a few times but we have never really had the opportunity to talk. To make conversation one day, I asked him what he was carrying. He immediately drew it from his holster and handed it to me with his finger on the trigger. I stepped to the side without trying to offend him and declined the offer. I told him I was just being curious but didn't need to actually see it since we were in a store and I might like it so much that I'd want to take it outside and shoot it (In an attempt at humor) He held it in his hands for a few seconds before re-holstering.
To me, it's kind of like offering your wife to someone just because they happen to mention how pretty she is.