AbleCommerce Shopping Cart Software

I ship orders worldwide. I use UPS and Fedex and USPS also some ocean freight. They don't all "Require" Harmonized Tariff codes. But if they are included on the invoice it helps thing go threw customs correctly. Some items are taxed differently then others based on there tariff code.

I have UPC's SKU's and Tarif codes for most of the products. What would be the best way to add them to the database? And make them print on some invoices but not all.

Thank you.

You can place the information in product custom fields. Have a look about how to use product custom fields with product.
viewtopic.php?f=44&t=9088
Then when printing invoices you can retrieve this custom information for the order items and make it available on the invoices.