What is the purpose of a 1 BTC deposit?

If you produce the product as promised, you can sell as many as you can produce for more than you're asking, so that's not it.

Is the deposit because you need the equivalent of $5,000 USD to fund this?   It seems your startup expenses will far exceed this amount.  In fact, it seems your expenses will far exceed your total revenue for 50 units at 8.99 BTC.

Not making much sense as a legitimate business...

Why is it that all these offers are always just on the verge of (but not actually) posting incontrovertible proof when they ask for funds?