In Spain, anything over 50 euro -included postage- is subject to taxes. BUT, it is impossible to stop every parcel that exceeds that value. I have had to pay taxes only twice: once that the seller sent me a seat and insured the box -a hint of value- and another one that the seller didn't fill out the customs form - I had to go to the office and show proof of value-. Another I received a box opened and closed with sticky tape from the spanish IRS. My guess was that the box was from a car rack and looked new, while the form stated "motorcycle used parts". I guess they opened it for inspection, and when they saw the handlebars they just close it and searched another one.
I believe they focuse in electronics: computers, audio etc. It costs the same time to fill the paperwork, while the taxes are much higher the higher the cost of the article.
Raul