It is easier to do a little customer service work in the first place than to try to appease a customer later. Communicate, communicate, communicate!When shipping the item let the customer know it was shipped and how. Include a freindly Hi! Include a thanks comment. Last but not least include a tracking#. It saves a lot of time in the long run because customers want to know this stuff anyhow. It cost 50-60 cents to purchase del confirmation from USPS and the cost can be included in the price of the item you sell. When shipping the item include the packing slip and also compose a sheet with helpful content such as how to process complaints with you and also the importance of feedback to both parties,  Announcement of sales, etc.

In addition, if you use paypal to ship your packages thru USPS the proof of delivery is 18 cents and if you send priority it is free. Also saves waits in line at post office.