Over the years as a Seller on Ebay, I have struggled with trying to keep shipping costs down for buyers. I have discovered some very easy "tricks to the trade"  and "Do's & Don'ts" which I will outline here:

• Whenever possible, use a flat rate Priority Envelope  (for U.S. destinations) which the envelopes cost  only $4.75 to ship & measures 12.5" x 9.5" and you can ship any weight in these...Great for heavy fabric, sheets, sweater or books, magazines. Remember has to close easily and you can secure over the adhesive with extra tape if needed to keep it closed.
• Flat Rate boxes are only about $9.00 to ship to any zone.  Will hold up to 70 lbs.! Terrific for a heavy pot, cast iron, heavy metal items, a lot of clothes or curtains. I have shipped up to 8 jeans and tops mixed in one of these. Clothes get very heavy, especially jeans and cotton baby clothes.
• Thank goodness for styrofoam.  Have friends or a business save the styrofoam packing for you. Buying this online can be very expensive. It is very lightweight and you can really safeguard breakables with this. Break it down to fit what you need.
• Empty egg cartons are always handy and terrific. (make sure these are clean..that no eggs were ever broken in them). They are very flexible and easy to cut to size you need. Really cushions stuff without adding weight to the parcel.
• Use empty paper towel tubes to fill in spaces in boxes. Breakables that are packed tightly and cannot bounce around will not break.
• Keep the empty rings to the large packing tape. Perfect to nest around a fragile ceramic top of a teapot lid for instance and tape into place.
• Approach a Furniture store in your area. They always have great packing items. Cushioned packing sheets and the heavy clear plastic coverings from upholstered furniture are my favorites.  I use the heavy plastic to cover large lots of clothes or fabric instead of a box which can add an incredible amount of weight for especially shipping to Canada or Internationally. Must be secured with strapping tape, and is a good idea to wrap the items first in a solid paper cover so the contents are not visible. But if you make 2 layers of this clear plastic the items will not show through. I sometimes buy the plastic drop cloths at Home Depot for this. Use the heavier mil weight.
• Don't be afraid to do box surgery. Always have sharp utility knife and scissors on hand for this. Just snipping away some of the excess flaps inside can shave off just enough ounces for your parcel to be under the 3 lb weight which really gets expensive when shipping to zones faraway from yours.
• Use the click and ship whenever possible.  You do not have to charge the full .50 for Delivery Confirmation to the buyer as it is free with Priority with click n ship and only .18 for First Class or Media. Delivery confirmation is a great way to keep track of your shipments for the buyer and prove that it did indeed arrive at the destination.
• Never send an item in a Priority Envelope or Priority Box turned inside out.  The Post Office knows their boxes and will charge your buyer the extra money and you want repeat buyers.
• Never send an item Media Mail that does not qualify for Media Rate. Look on the website for the requirements, as magazines with advertisements are not Media mail for instance.  And the Post Office has the right to open any Media Mail package to inspect the contents.
• Padded envelopes can be very pricey.  Use regular brown envelopes available anywhere for books, magazines, lightweight clothing. Add a small sheet of cardboard or wrap item in newspaper or bubble wrap to protect a book or items you do not want to bend or get corners nubbed. Reinforce with plain packing tape on all 4 sides so it will not split.
• Do a little more box surgery on Priority Boxes, for instance the cube boxes for a tall item....cut flaps off one end of each box, fit together and seal with tape. Great for tall items.
• Take 1 plastic grocery bag and stuff it full of newspaper or other plastic bags that you are saving for cushioning breakables or filling in spaces.

 

Hope this helps, and remember to add to your listing that you may use unconventional shipping / packing products to keep shipping costs down. I have had only great response to this, as most folks appreciate the lower shipping. It reflects how much they are willing to bid up to for the auction.