iirc you need 5 Infamy to trigger the event in the Trademond Adventurer Guild. You get that from various public Vice actions, like the Nephlune slave trade (which is a repeatable event you can use to get Infamy every 10 days), two of Hermann's H-scenes, or wringing money out of the farmers in Save the Crops (only if you didn't do the quest before Vice becomes available, and I'm not sure if taking the request from the Guild also precludes the reward negotiation after the quest). You can see Infamy under Compendium -> Aura -> Moral.
If you want to do the Vice path instead of the lewd path, you'll need 10 Vice, but can postpone the decision until you're ready.