I hope you stop going to flea markets. Immediately. Those are not your customers. Neither are your friends. (They can still be friends, just don't give them free products.) If your permit/license allows for wholesale, I suggest you approach stores and eateries that sell to your target market. @Pastrybaglady has some excellent advice about searching threads for more ideas.
If you enjoy chocolate brownies, you may like this recipe. Brandy Alexander Fruitcake is a rich chocolate confection with dried fruits (no candied fruits) and lots of nuts. It was always promoted in my bakery as, "The fruitcake for people who don't like fruitcake."
Why is it tacky for customers to know you use box mixes? If your customers like what you offer, they won't care if it's scratch or mix. If you want to reach a target market that prefers scratch baking, then look around for scratch recipes. Good luck in your business!