Sorry for the late reply, itch.io didn't notify me of comments for some time, it seems. If you want to get sold into slavery, you must go to the slums in Tarkas (available after you sleep for the first day).
Talk to Gaspar there (the same guy who offers to give you a tour of the city at the start). After you see the cutscene, you'll find him at the pub in the slums.
If you talk to him at the pub, he'll introduce you to a secret gambling den downstairs. Play at the blackjack table, lose at least 3 times, and touch yourself.
If you do all that, you can play blackjack 1 vs 1 with the boss, and if you lose too many times, you'll end up getting sold into slavery.