I don't really know what my ethics are, I'm conflicted, really. What if the person needs the buck they're making off it more than they need the item, KWIM? I guess I feel that, if someone wanted something to go to a charitable source, they would make the effort to donate it to one. For example, I Freecycle stuff I know my local charities won't take or can't really use, and I bring the rest to the charities myself.
And how do you know the people who pick up are actually in need anyway? I gave a lot (A LOT) of baby stuff I could have sold to someone who posted Wanted all over the local Freecycle groups. She was due with trips and seemed really in need, so I made a huge effort to pull all this stuff together for her. After she had the babies, she sent a link to a site she had made about the babies and highlighted the outrageously expensive, fully outfitted nurseries they had put together. So she could easily have afforded to buy the stuff I gave her.
And I don't exactly NEED the expensive shoes I just responded for

But I do really want them! So what defines a need anyway?
I don't know, I guess that's why I asked here. Devoid of any context, my ethics would be the same as if I spotted the item sitting outside a dumpster--mine to keep or donate or sell or trash if I felt like it. However, now I do have context, and as it turned out, there was even a file in the Files section about it (always forget about that thing), and they do request that you disclose if you're planning to sell stuff. So I won't be doing it. It's actually moot anyway, since I never get a single offer I respond about even though I am always polite and write complete e-mails (and not e-mails consisting solely of "Can pick up at 2:00" with no name, or please, or thank you, or niceties at all, argh!), and despite responding the exact same MINUTE that the post appears on the board. But that's a whole other post

Thanks everyone, for your input!