> Profit motive is all you need to be a smuggler, you don’t need espionage or anything else

What you need to be a smuggler is to avoid prison.

When one side is fully aware that you are a smuggler that they can rat on to the other side whenever they want, even a child could blackmail you.

So that's one (fairly realistic imo) pathway from smuggler -> to espionage.

This is a hypothetical anyways.

The core competency of smugglers is getting the goods delivered. Some smugglers are motivated beyond profit or avoiding jail.