Green’s Dictionary of Slang

killing a stolen dog that has not been advertised for (and that can thus be sold back to its owner). The skin is sold and the flesh used for dog’s-meat.

1781

G. Parker View of Society II 81: The people who practise this rig are dog-stealers. They call the dog a Buffer, from a practice among them of killing such dogs as no advertisement or enquiry has been made for; and this they call ‘buffing the dog,’ whose skin they sell, and feed the remaining dogs with his carcase.