The prisoners of the GULAGS sold as slaves.

Prisoners of the Revolutionary Government were transported to Siberia by trains in large numbers, thousands of men sent to serve long sentences. 

The bureaucrats and judges' expectation was that most of them would never come back. Many would die in the labor camps, others from hunger and torture. Others would die trying to escape, fleeing through the fields and galvanized and unpopulated forests. 

For all this there was no problem if a few hundred of them were simply sold by the soldiers to the farmers or to the nomadic peoples of Siberia. The younger, stronger, healthier prisoners were simply marketed, obviously naked, because the clothes on those polar lands were more valuable and necessary than their users.

Some were used as slaves on farms or to pull carts to the point of exhaustion and death. Once dead, or even dying, their bodies were often given as food to dogs.