Is there actually a key to understanding the problems in the other answer?

Inside means inside the container. In means within the structure.

Human bodies and tissues contain organs and blood but not the skin – the skin is the containing structure. Skin is the making of blood but not the ligaments and nerve cells. Where bullet is in the body if it hits the liver?

If a bullet goes through a body, someone taking the role as a surgeon could take it with a pincer. An internal surgeon might have to remove it, but if it went through the body, someone could remove it.

The shop has a more complicated containing structure including areas like a roof space and space behind the walls. So if you could in those spaces and not inside the shop, you could in those spaces and not outside the shop. Who is inside my shop? Inside means able to access the shop’s contents- things you can buy or utility areas such as behind the register or toilets or security areas.