The article says there are 500,000 items by that seller on Amazon. If you guess there may be 10 different variants of each search, that's 50,000 unique shirts.

The article says there are 500,000 items by that seller on Amazon. If you guess there may be 10 different variants of each search, that's 50,000 unique shirts. The engineering cost is probably pretty low compared to the fact they can stumble upon tons of valuable little niches this way.