SHIPPING ONE BOX AT A TIME...
Normally shipping one box through Priority Mail is the best way. Go to the Post Office and ask for a couple of their free Priority Mail boxes. Wrap the box in bubble wrap, and if the box is empty, put newspaper, plastic peanuts, or bubble wrap in the box. Put it in the Priority Mail box and seal it. You can use the adhesive tape already on the box, but also add some extra packaging tape on the ends just to be safe. Normally it is best to ship with the free Priority Mail box because postal workers won't damage their own box. If shipping with your own box use a sturdy box and be sure to once again fill the box if empty. Priority Mail will cost around $3-4 but should get to the destination in 2-3 days. If it is a trade postage costs will be the same, but if you use UPS overpack securely.
SHIPPING MORE THAN ONE BOX AT A TIME...
Normally 2-12 ounce boxes will fit in one box from priority mail but if it is 18 oz put one per box. Once again wrap the boxes with bubble wrap and fill the boxes if empty. If shipping more than 2 boxes it is usually cheaper to ship UPS. Since their is greater value with more than 1 box you may want to insure your box. It costs around $0.85 for up to $50.00 insurance with Priority Mail and UPS has automatic insurance for up to $100.00. Remember to tape all the ends shut so the box will not open.
SHIPPING COSTS...
How much you spend on shipping is up to you. If you do a little bit better than average on your part it will be appreciated on the other end and will lead to more deals with the person and greater feedback. THE GOLDEN RULE OF SHIPPING - Ship the package you are sending how you would want yours to be sent.