Apart from (obviously) including the lewd scenes, I would suggest making it clear in the shop conversations whether the customer is buying or selling. Just the word 'sell' added to the sentence isn't really enough especially when paying more attention to the woman than what they are saying (real world problems). I sold quite a few items at half price because I thought I was offering half the value to buy them.
Also, varying the text in the lewd scenes when they are added and having the descriptions match the NPCs.
There is game potential here though and a constant stream of both income and sex is never a bad thing, real world or game.