well, I guess there is no wrong/right way to do it, HOWEVER, I've found that when I ask someone about a certain something (whatever that may be) I know in my mind that I'm working on my plot/character and that this answer might help move my book along...so I feel guilty when I don't let on that I'm fishing for ideas or trying to flesh someone out.
I usually ask my question first, get the response, then fill them in...only because I'm still unsure of people's response when I mention I'm writing a book - my family is annoyed that I am so I assume most people would be.
However, I think it's still not ethically correct to get the info first. I might start out by saying, from now on, "I'm in the middle of working out the kinks in my plot and I was wondering if you knew anything about _____"...or something like that. It's not to say that you are really going to use that info in your book, but it might help you out of a tight spot, so I mention that too. I'm always looking for plausibility, so I usually have 1-2 people I can ask about certain situations.
So, in essence, I've answered my own question
HTH anyone else with the same Q's...