Final answer:
Key complementing offering techniques include building a foundation, making offerings pertinent, and being assumptive, although making complementary products cheaper is not always necessary. Monopolistically competitive firms can also increase demand through product differentiation, quality enhancements, and strong branding.
Step-by-step explanation:
The key complementing offering techniques include building the foundation, making it pertinent, and being assumptive. These techniques are important for enhancing the customer's purchase experience and increasing the likelihood of additional sales. Building a foundation means establishing a solid base of products that complement each other. Making it pertinent ensures that the additional offerings are relevant to the customer's needs. Being assumptive is about having the confidence that the customer will benefit from the complementary products and presenting them as such. Contrary to the options provided, making complementary products lower in cost than the initial purchase is not always necessary or advantageous, as it could diminish the perceived value of the offerings.
Aside from advertising, monopolistically competitive firms can increase demand for their products by differentiating their offerings, improving product quality, customer service, and engagement, leveraging social media presence, and through word-of-mouth by building a strong brand image.