When a buyer clicks checkout, the quantity of hops they've begun to checkout is immediately removed from the listing/displayed as "Sold Out." This isn't really true because the buyer may fail to complete the checkout for a variety of reasons: the buyer's credit card could get declined, they might lose their Internet connection, they could reduce the quantity they want to purchase, or they could just decide not to buy the hops before actually entering payment info.
If the buyer successfully completes a checkout, the seller gets an immediate email stating that a payment is processing...then another email once payment has cleared (ie the funds are actually verified).
If the buyer fails to complete a checkout within the 30 min window, the hops are returned to the listing and no longer appear as "Sold Out."
We have plans to change the sold out page to indicate the actual status so that buyers know there is still a chance to purchase the listing if the pending checkout fails; however, there are at least 6 months worth of higher priority improvements in the pipeline ahead of this.