Screen like crazy. They are swamped on the SF, even at a low volume store, and most of them aren't going to help a phone guest over a guest in the store.
Keep track of outs as you hear about them.
Refuse to do it if you can't have a zebra.
Remain pleasant, and lie when you need to--"sorry, he just told me they ran out." Everyone shops online, and they likely already know that we don't have what they want.
I have told guests that it could be as long as 15 minutes before someone can answer. Some people will wait, some won't.
Do walkie calls twice. "Call for small appliances on 2280. 2280 for small appliances."
And for the love of God, don't get on the walkie and ask for 12 days of Harry Potter socks.