Really liking this alchemist guild leader. The way I see from this chapter is that he was racial profiled because he was dressed nice and assumed that he was not part of the alchemist guild. Hayato must have mentioned that to the guild leader about it, how the adventure guild was throwing their weight around because the alchemist guild was not over charging them.
As for the MC, the guild leader sent him alone most likely wanted him to see that there are people in this world that would take advantage of him. The girl did not help as she was siding with the adventure guild.
"Hey, I broke your merchandise but I said sorry. Which mean I don't need to pay, right." If that is okay, then please. Since it was intentional, seeing how they ganged up on him afterwards.
The guild leader, did was right. He was emotionally abused and his merchandise was destroyed, so proper compensation is required.