Slavery. It was a dark element of the world in which we live and it also exists in the world of pathfinder. Despite the fact it exists, I rarely see it brought up in games due to it's controversial nature. While it may be mentioned here and there, it's true ugly face never comes up and that's most likely a good thing. However, despite this it is still a factor in the setting and I can't help but have a morbid curiosity about the topic of how slavery and characters related to it are handled in both Pathfinder Society and home games and exactly what level of exploration of the topic is considered socially exceptable...
I'm going to deliberately side-step the "Ever-falling Paladin(TM)" and "Failed Alignment System(TM)" side treks and stick to slavery in Golarion. I've seen quite a bit of it, even in PFS. I can't remember which scenario it was (one of the early ones), but part of getting the extra points for an Andoran was to identify that the main NPC's servant was actually a slave and then try to free them or something. I missed it and didn't get the points, but it was part of the scenario. There was another (that I barely remember) that had something to do with purchasing a slave in Absalom who is a princess or something.
The Legacy of Fire AP, while not PFS, has campaign traits where some of the PCs can start the game as slaves, eventually earning their freedom. It made for a great starting hook - some of the PCs are hired on, the others are slaves. Serpent's Skull was loaded with slavery notes. The whole place might as well be colonial Africa.
While the presentation of slavery differed in each of the examples above, they all had a "this is how it is" feel to them. But the main story in each case is not some kind of exploration or moral statement about slavery. That leaves the players and GM to make as much or as little as they want of it.