[dspillett]

Depends on local laws.

Also it can be difficult to reliably distinguish between an individual passing on a pet, a properly licensed breeder selling animals, and a bad actor doing the same (selling exotic animals, being an unlicensed breeder in jurisdictions where this is not permitted (generally or for particular animals), etc.). For this reason many advertising companies simply have a blanket ban on advertising any animal trading. Being more selective potentially leaves them open to legal issues if the selection process makes a bad decision and lets something illegal through, and that risk is not worth taking in order to allow (and therefore take a cut from) the more legitimate trade.