Audition agencys/monologues- What to avoid?

If your auditioning for a talent agency do they want or expect the talent to do A monologue from a play or is it okay to do monologues from monologue books/internet databases that have good contemporary monologues? Like do agencys have anything against just finding a monologue and performing it to your best ability or do they prefer their auditionees to do monologues from plays? Is it also better to have atleast 3 monologues prepared just in case? Also should one stick to their age group or if they can do a monologue of an older women is that ok too? For me this is a whole different ball game then doing student film auditions and plays so any advice, tips or personal experience that anyone might have had will be really helpful for me! Thank you