On me and my partner's site, http://www.mrairsoft.com, if someone orders something and doesn't click on "Return to Merchant" after making the payment, we don't get an invoice, which is crucial to processing the order. We use osCommerce (you probably figured that out based on the title). Can anybody identify the problem here?
It's osCommerce. I don't know why the programmers of osCommerce made it like that, but if the person doesn't return from the order then it is not recorded. Thus, you receive payments but don't know what was ordered. I don't know why osCommerce wasn't just built so that it recorded the order before sending the person to PayPal (or other processor). It could just tag it with some "unpaid" notification, so that the webmaster can manually update it to paid when there is an error in the process after payment.