As far as you and your buyers are concerned, that "authorize and charge" setting is functionally identical to the "authorize for the full amount" setting we recommend, but the former setting is only required by some other services instead of E-junkie cart and generates a bunch of meaningless error-log entries behind the scenes on our end and Google's end, which is why we recommend the latter setting in our documentation.
We know of no way to validate a buyer's payment account for an order total without also actually charging the account for that amount, but all of that happens on the payment processors' ends rather than ours, so it doesn't really concern anything at our end.
You may wish to inquire with Google, PayPal or other processors we support to see if they can put a transaction "on hold" or something similar that would verify the proper amount of funds are available and ideally also set that amount aside, but wait until you manually release the payment to actually charge the buyer's account and issue notification to our system that payment was completed, at which point we would then issue our thank-you emails with any download links.
The key issue here for our system is whether or not payment notification (IPN for PayPal, or API callback for Google) would still be sent to us after (and ONLY after) you release a payment manually, or if they'd just send us payment notification as soon as the buyer's account was validated for the order amount. In that latter case for digital products, you might as well complete payment automatically if the processor is going to trigger our issuing download links before you actually release the buyer's payment anyway.
At any rate, all of this would be a matter between you and the payment processor(s), as payments happen entirely at their end, and we do not formally support or recommend any sort of on-hold payments, so this would be up to you alone to set up without our help, and to troubleshoot if anything goes wrong.
