score:3
I've queried the Sokcho bus terminal from the BusTago in Korean language.
Left is the departure and right side is the destination. You can see two circles in the destinations, which says "Cannot book online: Purchase at the terminal". You cannot purchase a ticket using BusTago on the web.
However, there is another inter-city bus reservation system operated by T-money, so check the route if you can book it online with T-money's interface. Since there is no direct route from Sokcho to Pohang, you will need to book two tickets for each bus. Make sure you allocate enough transfer time to accommodate for unforeseeable incidents.