I had an uncompleted story set in my favourite slave-owning society of Xylae, with scenes in a market where slaves are made to perform partly as a warm-up before a sale and partly to show what they can do. You could vary this and have a more private sale in which the slaver brings a selection of his prime stock to perform for a particularly wealthy/important client(s).

In Xylae people are enslaved most frequently by having a rubber-coated steel collar locked on to them which begins to change their personality (I am big on MC elements). In this particular story, the slaver in question has developed a new collar which only begins to enslave the wearer once it is activated. He demonstrates this by activating the collar of a woman on stage and as she becomes a slave she performs more and more to demonstrate that, mainly FF action.

In fact all of this was background, the key focus was on a woman in the audience who has had one of these collars locked on to her, but it had not been activated. As the woman on stage becomes a slave she begins to recognise the woman in the audience as someone like herself and calls out for her to join her and the slaver's magic mirror (a lame concept okay) shows her how she would be once enslaved (i.e. dressed in rubber catsuit and thigh boots and completely servile), she flees the market, but the slaver is on her trail.