I liked this comment:
Communicate directly to the buyer when payment is received and when the item is shipped. While this doesn't directly apply to the collection of payment, it will go a long way to helping you encourage a future purchase from the buyer and ensuring that future transactions can flow as smoothly as the first.
What I don't understand is why neither eBay nor Auctiva automate the "Item Posted" email. I have a custom one I send from Auctiva, but I have to mark items posted, then select those transactions again to notify the buyer, which is slow & allows errors to creep in.