I am flying from NY to Amsterdam and I want to bring some spices with me. I plan on declaring it and putting it in my checked luggage. I know that if I had an unopened and sealed package, there would be no issue. However my spices are opened. How can I package them in a neat and proper manner so they don't get confiscated? I don't think a ziplock bag would work because they can't really tell if the spices are what I say they are.
Most likely without sealed original packing you cannot, there is no way you can pack them in such a way that customs will accept what is packed without original sealed packing.
Having said that I once carried pepper corns from china to Europe and declared them and was not questioned at all so your experience will likely depend on the customs persons helping you and other factors