For the purchased items I think it's fine, but for the items people are donating, the intent is usually that they be claimed by someone who plans to use them, not someone who plans to flip them. Though it does depend on the item; sometimes people give things away because they just want to get rid of them, especially with hard-to-move things like appliances. You can sometimes tell by the tone of the listing what the intent is, and I suppose it's up to each person's ethics whether they want to respect that.
It's a big controversy in communities like freecycle that attempt to maintain a certain charitable ethos and actively say that flippers aren't welcome, sometimes with exceptions for people who repair things (it's usually considered okay to take something broken free with the intent to repair and sell it, because that isn't pure flipping). Probably less controversial on Craigslist, which is a bit of a free-for-all.
I'm just now leaving an apt and put up stuff on CL. Some of it I'm willing to give for free (donated a bunch to charities, but they won't take everything)
As long as someone takes care of moving out of my place, I'm happy. If it goes to someone like this guy who flips to make a living and support his family, that's cool with me.
It's a big controversy in communities like freecycle that attempt to maintain a certain charitable ethos and actively say that flippers aren't welcome, sometimes with exceptions for people who repair things (it's usually considered okay to take something broken free with the intent to repair and sell it, because that isn't pure flipping). Probably less controversial on Craigslist, which is a bit of a free-for-all.