Zaroff says " If he does not wish to hunt, I turn him over to lvan... invariably, Mr. Rainsford, they choose the hunt." Why do Zaroff's visitors agree to be hunted? Is it a true choice? Explain.

No, it isn't really a choice. The prisoners can take their chances with Zaroff and possibly survive...... or have Ivan kill them without further consideration.

Zaroff's visitors agree to the hunt because they'd rather take the chance of surviving and winning the game as opposed to a sure death with Ivan. It is not a true choice because they are forced to either be killed on the spot or take their chances with the hunt.

Zaroff's "visitors" agree to get hunted by General Zaroff and Ivan, because if not General Zaroff gives an order to Ivan his servant to kill the victim with no mercy! So that is why Zaroff apparently gives the visitor a choice of getting hunted and possibly surviving three-day in the untamed wilderness.