There is a repeatable persuasion attempt at the Pearl in Denerim.
When first speaking with Sanga after clearing the mercenaries she will offer men, women, both, or a surprise. I personally picked women and she told me that they are 40 silver. I attempted to persuade her down to 20 and she meets halfway at 30. But after saying 30, I said nevermind. This was repeatable and just gave me the Silver Tongued trophy.
I am two points into Coercion and can't confirm what will happen at higher/lower levels.