How do you determine if a horse needs shoes or not? Grooming tips?

Just wondering! I am doing a little research! Also, I know how to basically groom, but I would like to know some tricks you do to get the flawless look for showing and every day grooming. I REALLY want to impress this horse's owner! She never rides or grooms this horse, so I really want to show her how good he looks when he is groomed. I might look at buying him because he is up for sale, so I do want to show her I am capable of meeting his needs! Consider this my trial! :)