Is that like a legitimate outfit? Like if I bought 1000$ worth of forever stamps would they actually be real? The USPS is ok with companies like this?
I think it's very likely to be legitimate based on my digging a couple of years ago. Note that it's not unusual to be able to buy stamps below full price – I used to see slight discounts on rolls and books on eBay
all the time. There are different reasons for this, different supply chains for discounted stamps, like businesses that have a surplus and need to unload them – they can't return them to the USPS after all.