Standard procedure (at least in Denmark) is as follows when buying from non-EU countries:
1) You pay the seller the purchase price and shipping costs by PayPal/creditcard/bank transfer/whatever.
2) If the items are caught in customs (most are), you'll have to pay local VAT (25% here - is it 20% in Holland?) of the full amount (meaning both purchase price
and shipping costs). For certain articles, there is an additional import duty that you must pay. On audio equipment this is usually ~3%, but if you're not sure, check it with a postal/customs office first.
3) In addition to these charges, whoever handles the customs procedure (courier, postal service etc.) will charge you a fee for handling the paperwork (The Danish postal service charges me ~10 euros depending on how many different articles are on the invoice, but couriers such as UPS and DHL may be considerably more expensive).
4) If no invoice is shipped along with the items, you will receive a letter from the customs authority asking you to state the contents of the package, the purpose of the import (gift, sample, merchandise, documents without commercial value etc.), the value of the shipment and perhaps even the country of origin for the items. VAT and import duty will (usually) not be added to samples and gifts.
5) The VAT and duties should in most cases be paid cash on delivery, but some couriers will deliver the package and then bill you later to save time and aid swift delivery.
I am certain the general principles are the same in Holland, but the rates will most likely vary a bit. Before deciding on a means of shipment, be sure to check the fees for processing the customs form first. AFAIK some couriers can charge 20-30 euros for this, which I think is outrageous (especially if the postal service will do it for 10
).
Hope this helps!
/U.