Parcel rates and packaging and everything else aside I thought  the poster clearly statet he charged 10 dollars for postage and sent the package as a large letter with stamps.     So the excess money was for his time to get to the post office.    The bottom line is any buyer would be upset if they thought they were paying 10 bux for postage and shipping and it came as a letter with stamps.   

Considering most people use the lowest price+postage search option,  maybe it would have been better to incorporate the extra cost into the item price,  or to list the item with free shipping.