Well, Flamestar, for the guards, that simply isn't their job. Since you want to talk to the Oracle, she requires a proper offering. Even in folk tales, you usually don't get something for nothing, and the more valuable the service, the more you must pay (a concept that will echo with mythic seriousness later). The offering itself you are expected to give is pretty simple, but she has accessory difficulties which leave her unable to discern the visions of Apollo. And, again, since you are the one who really wants her services, it is up to you to solve the problems... which lead into some great story lines.