Import duty is a fact of life. Here in the EU that's an easy thing to forget when importing something from outside the European Economic Area, as almost everything within the EEA is in free movement and attracts no import tax.
Some postal services will levy additional fees for handling the import duty for you, they have to pay customs then they invoice you, so they charge for the privilege. Fair enough. DHL, Fed-ex and UPS charge something like £9.50 to do this, your state-owned postal service will probably charge more. VAT is also levied by your government, here in the UK is it 20% for most things. But if you are VAT-registered, which you will be if you're a business, you claim this back. So you should be paying 0-20% of the value of the item in import duty, plus customs clearing fees, plus VAT.
Expecting your foreign supplier to under-declare the customs value is not trivial, he would be committing fraud by doing this, and as a business he's got better things to worry about than you moaning about your local laws. He'd rather not supply you than worry about his local customs authorities throwing the book at him.
If you want one party in the transaction to commit fraud, make sure it's you. Don't get arsey with your supplier because he's not willing to take any legal flak for you.