Slavery on Roshar has been shown to exist in many different forms.
Selling a woman of high dahn ... would be a risky gambit for a slaver. Most owners in civilized lands would require documentation of the slave's past, and it was rare indeed that a lighteyes was made a slave, aside from Ardents. Usually someone of higher breeding would simply be executed instead. Slavery was a mercy for the lower classes. 
However, there are plenty of small, independent cities in the Unclaimed Hills where Vorin rules governing the use of slaves is just a distant rumor.