That Worlds May Live by Nelson S. Bond

Standing there in the slave mart of Imperial Khundru, Gary Lane realized -- as millions of his human brethren had discovered in past ages -- that it is one thing to experience an emotional uprising when _reading_ about a situation, but quite another to be involved in that situation yourself.

In his university history classes Gary had read of the day when unenlightened Earthmen enslaved their human brothers, offering their flesh and services to hire on the auction block. From a purely rational standpoint he had disapproved of this barbaric custom, in this age happily abandoned. But now, here on a planet inconceivably far from the little world called Earth, he himself was not only _witnessing_ such a deal in human wares but was, indeed, one of the chattels to be auctioned!