Hi catbert,
There is a known issue that is causing an artificial amount to show up in the "Insurance" row on the Auctiva Checkout Details page when an Auctiva shipping insurance policy is generated for an item and it sounds like you are being affected by that. This issue should be resolved as part of our next site update that will take place in the second week of November.
If you check the payments that you received for these items, I believe you will find that your buyers actually did not pay anything extra for insurance.
If the item you purchased from yourself was posted through your Auctiva account while the "Use Auctiva Secure Checkout" setting was enabled, it should have been processed through Auctiva Checkout and you should have received an order summary email with respect to the transaction from Auctiva.
If you have any other questions about this, please feel free to contact our customer support team using the form on the following page of our site: http://www.auctiva.com/help/requesthelp.aspx
-Mike