The Apple Store is actually littered with well-hidden, high-resolution cameras. If you look hard enough at the ceiling, you will see some of them.
Inventory is so very tediously and meticulously tracked and counted that if something as small as a SIM card is missing, it will be found out within a day. They will find out why, where, and how within the next day after that. If it was stolen, no matter how sly you thought you were, your high-resolution picture will have a highly-skilled plainclothes security specialist’s name on it — don’t come back. If it’s big enough, they will find out who you are very quickly in partnership with local law enforcement.
Realistically though, most merchandise is noticed stolen in the moment. Think someone isn’t watching? They are, but they’re not going to chase you. The second you leave it will be documented thoroughly.