I think I answered this in another forum thread already, but just to reiterate for anyone reading here:
If a sale originated from eBay (rather than originating from an E-junkie cart), then our system would only find out about the sale after PayPal confirms the payment is good and complete, and that's when our system would log the transaction and issue an email with any download links or codes. If the payment was funded by eCheck (or in some cases an Instant Transfer after regular banking hours), then that would delay PayPal for some time (up to several days for an eCheck) before they could notify us that a sale occurred. This means that if an eCheck bounces or there's NSF on an Instant Transfer, there is no way that a customer could obtain your merchandise beforehand, so you're never left holding the bag.