To the folks confused at Yajin's poor treatment or the guild's "figure it out yourself" attitude, I'd recommend reading the WN, as it's pretty thorough. It's on Syosetu and Kakuyomu, but Kakuyomu seems to be the author's preferred platform (updates are there first).
A few things to keep in mind.
A) People are really racist here. Most have never seen someone with an Asian appearance. Several people assume that he is a cannibal, something he leans into later to be more intimidating. His own status has him with the titles of "monster" a "new kind of goblin".
B) Adventurers are stateless people. They aren't considered citizens of the cities they live in and aren't protected by most of their laws. The stereotype of an adventurer is someone who either can't hold down a real job or who is a criminal fleeing another jurisdiction. They are effectively the lowest caste of people wherever they go, and the only reason they aren't openly despised is because they tend to be armed and violent.
C) The adventurers' guild branches only very loosely cooperate with each other. In particular, smaller guilds don't bother raising up and investing in their members (such as by maintaining a library of monsters/herbs/etc or providing training) because successful adventurers inevitably move to larger guilds.
Now, you can disagree on whether the premises are plausible, but the WN rehashes these themes basically every time someone is a dick to the MC, such that it's beaten into your head.