Technically, I purchase the machine from them, then offer it off for sale here. Makes everything easier.
Does that mean that you bear the risk/reward of USD per bitcoin price fluctuations. That is fair to me, as long as you are willing to bear the loss as well as win the profit.
Yes, it's the risk we take. If BTC price takes a dive, we intend to hold the funds for refunds or until the price recovers so that we don't lose buying power (which is the goal) when we complete a purchase.