Generally speaking I have found that the type of carrier used has an influence on the likelihood of getting whacked for import duty. Nearly everything that has come to me via UPS, FedEx, DHL etc. has been hit with import duty at 6% of the value of the goods plus 17.5% VAT chargeable on the total plus the carriage. Then the carrier may add on an extra charge to cover the admin of collecting the duty!
I've never had duty imposed on any item sent via US Postal - delivered by Royal Mail - but I bet that will change now that I've mentioned it
As pasotibbs has noted, it's always good insurance if the sender can be creative in their description of the goods - 'Customer's goods returned from repair' or something similar often helps.
GJ