The cost of the product for the owner needs to be less than $150, or else this is not a store that makes a profit. $150 is the retail price  to the buyer, that’s why the change is $50 when $200 are paid. Losing the goods represents a cost of less than $150 for the owner.
The action of first stealing the $200 and then after a while giving it all back cancel each other. The two transactions are equivalent to the guy just entering the store once and jedi-mind-trick convincing the owner that he’s already paid $200. He then gets the goods and the $50 change in exchange for nothing.
So the correct answer is the loss totals $50+the cost of the product, and not $200!