The only way I won't drop this manga is "MC reluctantly rescue the dumb girl because his slave's request THEN immediately took off the dumb girl's collar and leave her alone (along with his slave if she took her friend's side) and search for smarter heroine(s)"
Holy shit wtf. This isn't what happened in the novel. This girl isn't that ungrateful/dumb.
They just leave her alone for a sec to make a payment or something and as soon as they take their eyes off her, that old dude threatens her with the knife and drags her away
Of all the possible things to change they had to choose this.