@yugiohkris @yldDavid @Umetsu
Jinwoo always had access to the Shop. He didn't need to unlock it.
The shop has 2 functions: BUY and SELL
The first time Jinwoo realizes that a shop exist is when he receives his first monster drop from an instant dungeon, the one where he got Rasaka's Fangs and fought a bunch of lycans if you remember. The items description says something about being able to sell the drops from lycans (was it the tooth? lol) on the shop, so Jinwoo tried calling out the shop. He was level 2 when he discovered the shop.
However, only the SELL function is available at first.
At level 20, Jinwoo unlocks the ability to BUY items - this is when Jinwoo killed the spider boss from the dungeon where he first met Yoo Jinho.