ShipScript has been an eBay Community volunteer since 2003, specializing in HTML, CSS, Scripts, Photos, Active Content, Technical Solutions, and online Seller Tools.
Below are instruction for items you plan to list (estimating costs), and for printing labels after they are sold (printing labels):
Estimating your shipping costs:
Flat rate shipping: Weigh and measure all the packages. Determine the shipping cost to zone 8 for each box. Add all the shipping costs together and list as one flat rate (same price to everyone). State in your description that you will refund the difference if the buyer is not in zone 8. You may want to block locations that are farther than zone 8.
Calculated shipping: This is much trickier, but can help get closer to actual costs without blocking locations. Find the near and far rates for each package and combine the near rates together and the far rates together to create a new cost-spread for the combined packages. Experiment with weights until you find a weight that can return somewhat the same spread of costs. You will not be allowed to charge more than what the buyer is shown at checkout, so err on the high side and let buyers know in the description that shipping is an estimate and you will refund if the actual costs are considerably less.
Printing your labels:
When you print your labels on eBay, print the label for the weight and dimensions of the first box. Then select the option to "print another label" for the same order, changing the weight and dimensions as needed, and purchase the next label.
Up to five tracking numbers can appear on one order. Label your boxes 1-of-2 and 2-of-2, and record what is in each box. Be sure to let your buyer know what will arrive with each tracking number.
Are you trying to list a set of books and need to estimate the cost of shipping in two boxes (my first example), or do you already have an order to split and need to print a separately tracked label for each box (my second example)?
