I tried listing a grill and a bunch of old patio furniture on the Craiglist "free" section the other day. I had no experience with the site, but the amount of hassle to try to sell these items, which are incredibly bulky, was really high compared to their value. Anyway, I simply listed them as sitting beside my driveway and that anyone who wanted was welcome to take anything they wanted. I chose a good weather period with the anticipation that they might sit outside for several days.
My son and I left for lunch and 45 minutes later it was all gone -- every one of 20 or so pieces. Piranhas probably take longer to fully strip a cow carcas.