A: HS classification is difficult for two main reasons.
First, the HS itself is very complex. Product descriptions are distributed among more than 5,000 headings and subheadings. The HS also contains section and chapter notes, which must be consulted in order to assign a proper HS code. Finally, classification is governed by a strict set of rules called the "General Rules of Interpretation" (GRI). It is hardly surprising then, that the average national tariff schedule is more than 2,000 pages.
Second, product descriptions in the HS do not usually match everyday product descriptions. For example, in order to properly classify an "electric toothbrush", it must somehow be matched to "Electro-mechanical domestic appliances, with self-contained electric motor, other than vacuum cleaners of heading 85.08. Other."