Seeing an Apple ad of a shiny image of a new iPhone imprints that image into the customers mind, even after they purchase and use the product. Their perceived value of their iPhone one year after purchase is greater than if they have not seen any advertisements, because they keep associating the product in their hands with the very high quality image on TV.
This is what's happening here with Mast Brothers chocolate. The high price itself can increase perceived value ("If it's expensive, then it must make me happy!"), appeal to values held by the consumer ("I support small businesses so I value the purchase more!"), and the packaging or storefront proximity ("Imagine how much value the product is since the packaging is such high quality, or the presentation on the shelf is high quality"). None of these have anything to do with the edible substance they're buying (the "end product").
In fact, I would argue that the end product matters the least for this particular product. Beyond some point, the quality of product does not affect its intrinsic value. Mast Brothers is beyond that point. The marketer therefore must use the above methods to further increase perceived value.
If you are a business owner yourself, you can choose to increase perceived value of your product in ethical or unethical ways. Some customers will detect unethical practices, some won't notice (such as people who don't read this article), and some won't care.