Kokua Line: Are half-price stamps for real?

Question: Every so often lately, an advertisement for 100 USPS Forever stamps at half-price pops up on my Facebook account. I have been deleting it immediately, under the tried-and-true advice that, “if it sounds too good to be true … ” Now I’m wondering if I am actually missing out on a legitimate bargain. I do love selecting the perfect greeting card for every occasion, and sending it off to loved ones.