When a decline response occurs and the "Amazon returned DECLINED for the authorization" note appears on the order, the order then moves to Accounts Receivable and sends an email to all users with the notification; "Process Amazon Payment". 

Yes, you receive the customers actual full email address just like you would for any credit card on your store.

No, not at this time.  Amazon Payments is not displayed when the cart contains an auto order item just like PayPal.

That is the entire fee for processing the Amazon Payments transaction.  Please note the fee structure is lower for transactions under $10 and the percentage also drops for merchants that process higher volumes of payments.

There’s a 14 day reserve after your account is established, after which you begin at Tier 1, which is a 7 day reserve.  Higher volume merchants can submit their account to be evaluated for Tier-2, which lowers the reserve to 3% of daily purchase volume and any outstanding refunds/claims.  More information about our full reserve policy is here: https://payments.amazon.com/help/Amazon-Payments-Advanced/Getting-Paid/What%27s-a-Reserve 

Amazon Payments does not replace your merchant account which allows direct credit cards.  What it does allow is the customer to login to their Amazon account and use the addresses and credit cards they have on file with Amazon.  It gives the customer a very fast way to check out.

Use the refund functionality within UltraCart just like you would credit cards.  It all happens automatically.

Amazon leverages all of it's anti-fraud technology while processing payments.  There is still a chance of a chargeback scenario similar to any other payment method.  Amazon will contact you via the Amazon Seller Central web interface if there is a disputed charge.

When properly configured, Amazon Payment orders stay in the pending clearance section of UltraCart for a few minutes.  The orders go through the Confirm Order -> Authorization -> Capture.  If you have live orders staying in the pending clearance section longer than that then you failed to configure the Amazon Payments Instant Payment Notification feature in step 3 of the configuration tutorial.  If you fail to configure this UltraCart will check all pending clearance orders at 9AM EST and release them so that they will still flow.

Yes (see also the following Q/A regarding shippable items and upsell after)

The way the Amazon payments integration works, it requires the initial checkout to contain a shippable item in order for an upsell after that requires shipping details to be triggered.

YES.

If your button disappears when you un-check the sandbox testing setting, your account may not have a hold on it that is preventing the live mode form functioning. Please contact Amazon customer service to ask them to review your account and confirm that is ready to function in the live mode.

No, Amazon will detect that the two accounts are associated because of the email or credit card number.  You should use another unrelated Amazon account other than the business such as an employee's personal Amazon account.