One of our customers discovered how to complete customs processing himself when importing Japanese tea into Spain by postal mail. He purchased 6288 yen worth of tea + shipping and instead of paying €58, he only paid €13 in fees.
(Disclaimer: We take no responsibility if you decide to attempt this yourself.)
This is the guide he followed: https://www.adslzone.net/reportajes/e-commerce/evitar-pagar-aduanas-adtpostales/
here is another forum with instructions and buyers commenting on their experience: https://myfigurecollection.net/blog/46101
Please post your experience in the comments (in Spanish is okay) for other customers if you attempt to do this.
memo from a recent customer (April 2021): “Links are a bit dated as it seems, and the procedure today was relatively straightforward and fully online, just that all in all it took a lot of waiting. Amount that I had to pay corresponds to standard 21% VAT plus 6€ processing”