Currently de-cluttering so have joined several local "re-use, recycle" Facebook groups to get rid of stuff I can't be arsed to sell.
Recently a fight broke out because someone sold on an item they'd received off the page for free. It's not in this particular groups rules but admin agreed it was "not in the spirit of the group" (and has amended the rules).
The person who gave it away felt it was unfair because they had given it away with the intention of helping someone unable to afford the item (a running buggy). The person who sold it on argued they'd done work cleaning it up and making repairs and therefore 'deserved' the profit. They've been banned from the group.
I'm neither person but saw the argument unfold. I think I'm on the side of the seller - if they'd "upcycled" a piece of furniture I doubt anyone would think it wrong.
So:
AIBU - Free stuff should never be sold on, it's cheeky.
YANBU- it probably depends on the item, but it's fine.