I don't trade much through forums other than with people I already know (either via previous sales/purchases, or from conventions). But I do have a nice story.
I got back into collecting TFs in August/September 2005. And as naïve as I could've been then, my very FIRST forum-based toy transaction in my adult collecting career was a trade with a guy I never met, but I ran into on the old TFans boards, as we were able to find different waves of the toys back then.
He ended up e-mailing me a video of him slipping a $10 bill in one of the boxes (to account for the value difference in the trade), and we both shipped out our stuff. Trade went through without any problems.
And to this day, the dude I traded with is still a great friend of mine. Props goes out to Cliffjumper69 on the boards here.