idk how it works on facebook, but ik on other sites (i use kpop usa, and i really like them) you order it, put in your card info, and you'll get the album abt a week or so after its release. it's a good way to make sure they don't sell out. i'm not sure if kpop usa does it, but some places have an option where you can pay it installments. hope this helps!
ummm, facebook or insat - buying from social media is not good choice.
of course i also get the pre-orders but anyway buying from websites are better for your money.