How does one get inventory for a new LGS?

My brother in law is very involved in Pokemon, YGO and Sports trading cards but knows little to nothing about MTG. He is considering opening up a brick and mortar card shop soon and I've been trying to tell him that if he can get enough floor space for tables, he could easily attract MTG players by being on the companion app and running events, pre-releases etc, which (im my experience) always translates to me spending more than I should on cards.

However, I am curious how a LGS goes about sourcing sealed products for their shelves as you get your store going, especially if you are not super familiar with Magic.

I see that there is the Wizard's Play Network (https://wpn.wizards.com/en/news/how-apply-wpn). Does this allow you to get cards directly from WoTC distributors? Otherwise, are you stuck buying boxes from TCG and selling them for way above MSRP?

Any info on this would be helpful! Thanks!