This would be a winning strategy for the seller, given that the value of the product is less than what they charge.

I don’t think so. They’re still making the exact same revenue per sale on average. The cost isn’t relevant here, another way of looking at it is in the case the customer pays nothing they’ve lost the cost of the goods and the profit they would have otherwise made, so it evens out.

It works out well for the seller if, by providing the option to gamble on the product, they increase sales, which I would guess it would (at the expense of being morally grey).

You’re right actually, come to think of it. Their revenue would be the same overall.