You're not actually trading for these things per se, right? You're just much more willing to share homebrew with the people that hook you up with these things is what I'm reading.
Since bartering with homebrew is illegal, at least here in the US of A.
But that said, I'm much more gratuitous with my homebrew to people who let me borrow tools, textbooks, or let me crash at their place after a night out than I am normally. I figure I can return the favor way down the road, or while it's still fresh on my mind just say thanks with a 6er or so. Most people don't mind that kind of thank you note.