In the story "The Ransom Of Red Chief" what is the kidnappers' first clue that the Dorsets are not alarmed at their son's kidnapping?

This story is a comic story of reversals - that is the way things are or happen are directly opposite from what one would expect.

For example, the lazy rural town of Summit is as flat as a pancake, with no summit or vantage point in sight.

The kidnappers supposed that Southern families would be more protectionalist towards their children, but they learn rather quickly that this is not the case, at least with the Dorsets.

They want to extort money from Mr Dorset by kidnapping his son, but true to his name (his first name being "Ebenezer," the same first name as Dicken's Scrooge!), they confront a hard-nosed penny-pincher greedier than they could ever hope to be!

They should have "flaired the scent," so to speak, when the Dorsets were in no hurry to reply to their ransom note. That should have been a clear sign that they were not typical parents,  besides themselves with worry over the whereabouts and well-being of their progeniture. Instead, they take a "station break" before offering to take their pest of a son back -  that is, after being paid a "compensation" for their trouble, of course....