Without a pet: "I'll train even the most stubborn pets to do incredible tricks! So bring your pet next time!"
With an egg: "G'day mate, come back when your egg has hatched!"
With a pet: "G'day mate, want me to train your animal? Alright let's begin!"
With a pet that knows every trick: “Looks like your pet already knows every trick in the book!”
With a pet that is too young: "I want to train your [XXX]. But it's just too young to learn any more. Come back when it ain't so little."