POSTAL CHARGES...
Postage is always tricky to set!  Where in the world might you have to send your art?  Which postal services to use?  All I can do is to give the benefit of my own experience.

Setting the postal charge: You don't want to be so expensive that you lose sales - nor to be so cheap that you lose money! You need to find a suitable compromise.  In my case I analysed a full year's invoices to arrive at a postage charge that suited most destinations and packaging methods.  I ship prints rolled in tubes by preference and no longer offer matted prints from my websites.  But I do still ship multiple prints packed flat (between two sheets of 2mm MDF), which is equivalent to shipping a mounted print.

Be prepared to lose money on some shipments - you will make up for the loss on others.  For example, if you lose a little money when shipping 3000 miles away, you'll get it back when shipping locally at the same rate.  The "trick" is to make enough on international shipping but to not be too pricey locally.

Here in the UK I ship tubes worldwide by Royal Mail "printed paper" service (must be under 2kg). I have my shopping cart set to a post charge of £2 per item plus a shipping charge of £2 - I lose a little about 30% of the time.  But it only takes one UK order for a couple of prints to redress the balance.  Remember that if your customer orders more than one print it will cost you almost nothing to ship the second one.

To summarise:
• Weigh your products and estimate your expected sales overall.
• Set your postage charge to cover the average cost of sending that product.
• Keep an eye on results and inform us if you need to adjust your charges.

SHIPPING & HANDLING...
Optional: This is the cost of your packaging and incidental expenses.  It is charged once per order.  If you have two forms of packaging, charge for the higher of the two.  The "extra" will compensate you for your losses when shipping to the back-of-beyond on the other side of the world.

Personally I keep two lengths of 3" diameter tubes in stock (18" and 24") and sheets of 2mm MDF pre-cut to 18" x 24" (MDF is similar to Masonite/hardboard, smooth on both sides).  The MDF is slightly more expensive so I base my packaging costs on that.

How is Shipping charged?:The "post" charge is applied to every print (or other item) ordered.  The "shipping" charge is applied only to the first item ordered. So (using example prices only) the first £10 print ordered is: £10 + £2 postage + £2 shipping. All additional copies are charged at £10 + £2 postage. If you don't want to set a "shipping" charge leave it blank. In that case every print will be simply charged as £10 + £2 postage.

To summarise:
• The charge is optional - you can omit it if you prefer.
• Find a regular source of packaging and make a note of the cost to you.
• Charge for the most expensive form of packaging if using more than one.
•  And don't forget to add in incidental expenses....
• parcel tape
• labels
• polythene liners... etc
• The cost of driving to the Post Office and back. I live 6 miles from the nearest branch - 30 mpg @ £5.94 ($12) per gallon = £2.38 ($4.75) per round trip!

UPDATING...