Realization

Among the three kinds of city guards, the Inner City Guards were the most hated, and the weakest in terms of overall strength. 

The Wall City Guards has a member requirement of having at least an F-Apprentice Rank along with their summons. The Road City Guards has a member requirement of having their Summoned Monster at least, E-Elite Rank. 

On the other hand, to join the Inner City Guards, one must only need to have a summon that is at F-Apprentice Rank. 

The guard that was trying to scam them only has an X-Mortal Rank while his Monster, Brown Viper, is already at the F-Apprentice Rank.

And being stared down by Ban, who was a Rank higher than him made the guard shiver in fright. Ban did not show his strength yet, but his voice and the color of his eyes alone already made the guard scared shitless. 

Not to mention, his beloved Brown Viper who was already at F-Apprentice Rank was easily thrown away by Eva, which made him even more scared.