Forever Stamps at 50% Off?

I see some sites claiming to sell USPS Forever stamps at 50% off. One thing that makes me suspicious is that one site lists the regular price for 100 as $55 instead of the current price of $66. Now, the stamps offered do claim to be from prior years, say 2019, when the price for a stamp was lower when originally issued. But as Forever stamps that shouldn’t matter…

I won’t name any of them, but they can be easily found as ads at the top of Google search results for first class stamps. Are these a scam or a deal (assuming one is in the need of stamps)? Is there a catch? Seems kinda sus to me.

I don’t really know, but selling USPS stamps seems sketchy.