The “and that’s not all have some steak knives” approach works sometimes but not every time. “Sellers believed that spending more money to add features to their already strong propositions would strengthen them further, yet on each occasion adding an extra feature served to cheapen the overall proposition resulting in potential customers saying they would pay less.”
Cialdini suggests “rather than investing additional resources to add a small extra feature [e.g. steak knives] for every customer, it might be wiser to invest the same amount in a more significant extra feature for fewer selected customers”.
The blog post from which I took the quotes has been removed, but you can find the details (and more) in the the Small BIG by Cialdini and his colleagues.