 How does Johnson trick the duo into paying for things more than once?
Paying no attention to them, it was carrying a case of liquor in two hands, six siphons in two others, and a broom and dustpan in the remaining pair. The interplanetary con-men drank noisily, asked for more, until they had drunk eight glasses. Liquor's free with every chaser." "When there ain't many customers, you gotta make more on each one. It's bitter as some kinds of sin before it's purified. "Friend," said Harvey, taking out a wallet and counting off eight five-bucko bills, "here is your money. What's fair is fair, and you have put a different complexion on what seemed at first to be an unconscionable interjection of a middleman between Nature and man's thirst." "On account of the quantity, I'm able to quote a bargain price. Shucks, boys, it hurts me more to charge for water than it does for you to pay. The planetoid man worked the pump while the mayor intently watched the crude level-gauge, crying "Stop!" when it registered the proper amount. Then Johnson rubbed his thumb on his index finger and wetted his lips expectantly. "Now do you see, my hot-tempered colleague?" said Harvey as he and Joe picked up buckets that hung on the tank. "Johnson, as I saw instantly, is the victim of a difficult environment, and must charge accordingly." "Just the same," Joe griped, "paying for water isn't something you can get used to in ten minutes." In the fragile forest, they soon came across a stream that sprang from the igneous soil and splashed into the small pond whose contents, according to the mayor, was theirs for the asking. They filled their buckets and hauled them to the ship, then returned for more. He uses only one pool, the sweet one! Johnson's eight-foot son, topped by a massive roof of sun-bleached hair and held up by a foundation that seemed immovable, had obviously been born and raised in low gravity. Harvey studied it worriedly, put his own hand somewhere on it, swallowed as it closed, then breathed again when his fingers were released in five units instead of a single compressed one. "What do you mean, once ?" demanded Johnson. "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.
 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.