In "The Ransom of Red Chief" by O. Henry, how does Ebenezer Dorset know Johnny is giving the kidnappers a hard time?

Johnny's father Ebenezer knows his son Red Chief must be giving the kidnappers a bad time because he knows the boy is a hellion. Ebeneezer shows this in his reply to the ransom note, in which he writes:

You bring Johnny home and pay me two hundred and fifty dollars, and I agree to take him off your hands. You had better come at night because the neighbors believe he is lost. And, I could...

Johnny's father Ebenezer knows his son Red Chief must be giving the kidnappers a bad time because he knows the boy is a hellion. Ebeneezer shows this in his reply to the ransom note, in which he writes:

You bring Johnny home and pay me two hundred and fifty dollars, and I agree to take him off your hands. You had better come at night because the neighbors believe he is lost. And, I could not be responsible for what they would do to anybody they saw bringing him back.

When the two kidnappers return the boy to his father that night, Bill asks how long Ebenezer thinks he can hold his son while they make their getaway.

"I'm not as strong as I used to be," says old Dorset, "but I think I can promise you ten minutes."

Ebenezer Dorset seems to feel some compassion for Bill and Sam because he knows what they must have been going through. He has been having the same problems with Red Chief for years. As a result, he has become a patient, philosophical man, as one might expect when meeting the parent of a boy like Johnny, who is always causing trouble and who never seems to run out of energy. Ebenezer shows no ill will towards the two kidnappers. It seems he believes they received the punishment they deserved.

It is unclear why Ebenezer thinks he is entitled to collect $250 for taking his own son off the kidnappers' hands. Evidently, it is a question of the son's value. Bill and Sam estimate that the boy is worth $1500 to the father, but the father's insistence on receiving $250 implies he does not value his son and instead sees him as a burden. Ebenezer knew the kidnappers have no way of getting rid of Red Chief unless he agreed to take him back.