Along with theft of pets those who seek to find dogs or cats to use in their dog-fighting endevors CraigsList is the most widely used place to aquire either a dog for fighting or to be used as bait in dog training.
Contributing to an on going and horrific problem should be CraigList concern out of decensy and respect for the commnities at large.
Most people are not aware of the problem or the consequences of listing their pet as FREE.
A re-homing fee usually deters the abusers as paying for these animals is not profitable for them.

Another problem is the equine for FREE.....they are rounded up by "kill buyers" who ship them over the border to slaughter houses in Mexico and Canada.  Again most people are not aware that their once loved pet could very well be destined for such a horrific and cruel end.