everyone and there mothers are making these loving loot box things. It must be like creating money out of thin air or something.
It practically is, provided you have the money to start up to begin with.
You need enough money to acquire some decent quality items, and ship them out to a few hundred people initially, while you generate interest.
And then the amount of customers you have starts to grow, and you can start to lower the quality of the items you provide (particularly clothing items, which you'll be able to source at a much lower quality than toys/figures).
Generally the cost of the products and the shipping should be smaller than the cost you charge customers. Building you a small profit.
And as the customer base increases, and the quality of items lowers, you start to make much more significant profits.