Hi! I just finished reading. Here's my guess: Yes. Johnny is that con artist. Calahan guessed everything about the medicine and the murdered quack correctly after he got his note back. Calahan probably sent the note to Johnny's mom and if she was alive at all, she would have replied with something knowing her son is doing well. But instead, he got the same note back, which means Johnny's mom is long dead.
Calahan hinted that he knew Johnny's mouth has been used to do the oral sex before. So, I think that Johnny is always gay (bear chaser type, to boot, according to IAGO, the author

guys.... i fear I may be stupid but...
was johnny the grifter or not???
also... what did he lie about??? and the note Calahan received/sent???? I dont get it. I fear I am too stupid send help-
otherwise
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