If each of us ran a full costing system you would realize that you are not truly recovering your eBay and PayPal fees in your postage or delivery charges.
Example in point, you must cost the expense of the envelopes, the time to purchase your envelopes, complete, print and attach mailing labels, time and expense to take packages to Post Office etc.
Similarly, your costs in time to list items, answer emails etc. If you were paying employees to do this, their hourly rate would be factored into the cost so that you could arrive at a true 'per envelope' mailing cost and true management costs in running the business.
You may be calculating what your eBay and PayPal fees are and allocate a shipping charge sufficient to recover those fees but you are writing off other costs (some hard costs, some soft such as your personal time) at the same time.
In the accounting world, marketing and finance costs (eBay and PayPal fees) should be something that you are covering in the selling price of your item. If you need to recover eBay and PayPal fees from shipping costs in order to make a profit from your selling price, then it is time to look for other items to sell, you are living on too tight a margin to make a buck unless selling hundreds of thousands of those items per month.
In the accounting world, you are supposed to charge GST on your shiping charges for goods sold within Canada, so ideally, subject to an audit, you could be liable for paying the Government 7% on that "padded" shipping amount that you charge your Canadian customers.
I just believe that you should always look at what you are selling and if you cant make a profit off of the selling price, move on and sell something different.
Just like in WorldCom or Northern Telecom, you can only play with the numbers so long before people realize that you arent making the profit you say you are.
In this case, we are only fooling ourselves by showing a profit from sales when we have to allocate some of the fees associated with selling the item to shipping charges.
Malcolm