Como @EikePierstoff e @Kao mencionaram, isso é quase certamente "A Loja dos Mundos", de Robert Sheckley, e coletado em sua antologia de ficção curta > do mesmo nome
Você pode ler (algumas delas) on-line aqui ;
Mr. Wayne came to the end of the long, shoulder-high mound of grey rubble, and there was the Store of the Worlds. It was exactly as his friends had described: a small shack constructed of bits of lumber, parts of cars, a piece of galvanised iron and a few rows of crumbling bricks, all daubed over with a watery blue paint.
“I’ve heard about your store from friends,” Mr. Wayne said. “Then you know my price,” Tompkins said. “Have you brought it?” “Yes,” said Mr. Wayne, holding up his parcel. “But I want to ask first –” “They always want to ask,” Tompkins said to the parrot, who blinked. “Go ahead, ask.” “I want to know what really happens.” Tompkins sighed. “What happens is this. You pay me my fee. I give you an injection which knocks you out. Then, with the aid of certain gadgets which I have in the back of the store, I liberate your mind.”
“Your mind, liberated from its body, is able to choose from the countless probability-worlds which the Earth casts off in every second of its existence.”
O dispositivo é capaz de transferir a mente para uma realidade alternativa por exatamente um ano, ao custo de dez anos de vida do usuário.
If you have been harbouring a secret dream of murder –” “Oh hardly, hardly!” cried Mr. Wayne. “– then you will go to a world where you can murder, where you can roll in blood, where you can outdo de Sade or Caesar, or whoever your idol may be. Suppose it’s power you want? Then you’ll choose a world where you are a god, literally and actually. A bloodthirsty Juggernaut, perhaps, or an all-wise Buddha.” “I doubt very much if I –” “There are other desires, too,” Tompkins said. “All heavens and all hells. Unbridled sexuality. Gluttony, drunkenness, love, fame – anything you want.”