"If this Joker guy was Soh's Mart, he'd have had us bring a bigger car"
I think this hints to the backstory that the Joker made them think that Soh's Mart (probably the fictional equivalent to Wal-mart in this world) was backing them and that he was part of it somehow. That makes sense why they would follow him, since it is kinda sus to follow just "The JOker" when you don't know anything about him.