Question of the day: If you go to online forums to get sources or quotes, do you then contact the person and interview them by email? Or can you use a quote that they said in answering your question straight on the forum? And then just contact them to get their real name and permission? How do you handle asking questions on an online forum?
To answer your first question: yes, if I saw someone in a forum who might be of interest, I would contact him/her off-board and then set up an interview. I would never, ever, ever just take a quote and assume that the person would be okay for me to use it in a more public forum, like an article. I'm not even sure, to be honest, if this is legal, especially if it's a membership board. (Well, it's probably legal, but I don't think it's particularly ethical.) People post things on forums that are often thought of to be "for forum eyes only," and violating this is unacceptable, in my opinion.
The best way to garner sources from a forum, in my opinion, is to a) first check with the forum moderator and ensure that you can post something looking for sources and b) post a separate thread stating what you need and what you're looking for. Then, people don't feel as if you're capitalizing on something they might not want to discuss further with you (if you contact them unsolicited about something they've previously posted). Forums can be tricky, and they're not my first choice to find sources, to be honest. Some moderator and subscribers don't want to feel like journalistic prey, and there certainly is that line you toe between respecting people's privacy and getting your article written. So, all in all, post your own thread and let them come to you.
Just my two cents. How do others out there handle forum trolling?