Answer:
Lessens; Less.
Step-by-step explanation:
Porsche has enhanced power over buyers because its strong reputation makes buyers more willing to pay a premium price. This lessens rivalry, since buyers become less price-sensitive. This mostly happens in premium end product where customers want to pay as much brand want to charge, where customers are not much concerned about the other brands, they have to have the products of certain brands at any cost which lessens the rivalry because customers are very much less price sensitive. As we have seen here for Porsche, same is the case with Apple, where customers want to pay higher for its iPhone and McBooks.