 How does Johnson trick the duo into paying for things more than once?
"On account of the quantity, I'm able to quote a bargain price. Then Johnson rubbed his thumb on his index finger and wetted his lips expectantly. "Just the same," Joe griped, "paying for water isn't something you can get used to in ten minutes." "You'll find everything you want in the back room," Johnson said frantically, "sulfopyridine, mustard plasters, rubs, inhalers, suction cups—" "Relics of the past," Harvey stated. "'Course, I'd expect a considerable reduction if I bought a whole case," said Johnson.
 He is dishonest. He offers something for free, without mentioning the actual price of it or that there even is a price.
 He strong arms them into buying with his son.  He is dishonest. He offers something for free, without mentioning the actual price of it or that there even is a price.  He takes advantage of their good will.  He doesn't trick anyone - he is an honest man that is running several jobs.