Before Amos had time to ask if there was a piece of land he could buy for his work and home the constable spoke up. “I’m only doing my duty, when I tell you you’d best be gone from this town.” Amos smiled. He knew the formality of the warning and the reas

From the text:

“It might be a fine thing for the tanner,” the constable responded, then he looked at the Negro more sharply— the leather breeches the man was wearing might have been worn by gentry and he carried a pouch that was a pretty piece of tooling. However, no matter what the man’s trade, the constable knew his duty would be undone if he did not endeavor to send him away.

The prejudice that still existed in the town forced the Constable to warn Amos as a form of protocol. He didn't care if Amos moved into the town, and he also knew that Amos' trade was much needed. He simply did what was expected to save face with those who would not approve.