E. Everett Evans 
Alien Minds 

"Were you looking for a roch, nyer?" An oily voice spoke up just by the elbow of George Hanlon. "I have some excellent ones here, sir."
"Yes, nyer, I want several, if I can find ones to suit me, " the young man replied. Nor could anyone, glancing at him, know he was not a native of this planet, Szstruyyah, which the Inter-Stellar Corpsmen, in self-defense, called "Estrella." For the cosmetic-specialist who handled the secret servicemen's disguises had done a marvelous job in transforming the blond young Corpsman into an Estrellan native.
Hanlon continued looking into the outside cages containing these tailless roches, the Estrellan equivalent of wild dogs. "I want eight, all as near the same size, coloring and age as possible."
"Eight, did you say?" the merchant looked at him in astonishment. Hanlon, carefully reading the surface of the man's mind, sensed the conflict there between the ethics his religion and philosophy had taught him, his natural love of haggling, and a desire to make as much profit as possible. But he could not sense the slightest suspicion that the man confronting him was not another Estrellan…