Custom duties, also known as import duties, are taxes imposed by governments on goods and services imported into their country.

The main purposes of custom duties are:

1. Protectionism - Custom duties are used to make imported goods more expensive compared to domestic goods, protecting local industries and jobs from foreign competition.

2. Revenue Generation - Import duties provide a significant source of revenue for governments, helping to fund public spending.

3. Trade Regulation - Custom duties can be used to restrict imports, either for economic reasons or to enforce trade policies and international agreements.

The specific rates of custom duties vary greatly by country and by product category. Duties are typically charged as a percentage of the value of the imported goods (ad valorem duty) or as a fixed amount per unit (specific duty). 

Custom duties are applied at the point of entry into a country, with importers required to pay the relevant duties before the goods can be released. Governments often maintain complex tariff schedules with hundreds or thousands of different duty rates.

In addition to the base duty rate, there are often other fees and taxes levied on imports, such as sales taxes, excise taxes, and processing fees. The total cost of importing a good can be significantly higher than the base price due to the cumulative effect of all these charges.

Overall, custom duties are an important trade policy tool used by governments to shape the flow of imports and protect domestic industries. The specific rates and application of duties can have major impacts on a country's economy and trade relationships.

Custom duties can have significant impacts on international trade and economic policies.

Here are some of the key ways custom duties influence trade and economics:

1. Protectionism:
   - Imposing high tariffs on imported goods makes them more expensive compared to domestically produced goods.
   - This protects local industries from foreign competition and supports domestic job creation.
   - However, it can also lead to retaliatory tariffs from trading partners, sparking trade wars.

2. Revenue Generation:
   - Custom duties provide a major source of government revenue, especially for developing countries.
   - This revenue can be used to fund public spending and social programs.
   - However, over-reliance on tariff revenue can discourage trade liberalization.

3. Trade Negotiations:
   - Custom duties are a key bargaining chip in international trade negotiations.
   - Countries attempt to gain favorable tariff rates for their exports while protecting sensitive domestic industries.
   - Tariff reductions are often a major goal of free trade agreements.

4. Economic Distortions:
   - High tariffs can lead to economic inefficiencies, as domestic producers face less competition.
   - This can result in higher prices, less innovation, and a misallocation of resources.
   - Tariffs also create administrative burdens and compliance costs for importers.

5. Geopolitical Factors:
   - Custom duties can be used as a foreign policy tool, imposing barriers on goods from adversaries.
   - Tariffs may also be applied to exert political pressure or retaliate against other countries' actions.

6. Developing vs. Developed Countries:
   - Developing countries often rely more heavily on custom duties as a revenue source.
   - Developed countries tend to have lower average tariff rates, having liberalized trade more extensively.

Overall, the strategic application of custom duties is a critical component of countries' economic and trade policies. However, there is often debate around striking the right balance between protectionism and free trade.

Custom duties or import tariffs can impact a wide range of products and industries, but some of the key product categories include:

1. Agricultural and Food Products:
   - Agricultural goods like grains, fruits, vegetables, dairy, and livestock are often subject to high import tariffs.
   - This helps protect domestic farmers and food producers from foreign competition.

2. Manufactured Goods:
   - Tariffs are commonly applied to imported manufactured products like electronics, machinery, vehicles, and consumer goods.
   - This supports domestic manufacturing industries and jobs.

3. Raw Materials and Commodities:
   - Import duties may be levied on raw materials like metals, minerals, and energy products.
   - This can favor domestic extraction/production of these commodities.

4. Luxury/Specialty Goods:
   - High-end consumer goods like jewelry, watches, fashion items, and premium alcohol often face significant tariffs.
   - This allows governments to capture revenue from wealthy consumers.

5. Sensitive/Strategic Industries:
   - Tariffs can target industries deemed strategically important, such as defense-related products.
   - The goal is to maintain domestic production capabilities in key sectors.

6. Developing Country Exports:
   - Developing countries may face higher tariffs on their exports to developed markets, limiting market access.
   - This is a source of friction in global trade negotiations.

The specific products targeted and tariff rates applied can shift over time based on a country's economic priorities, trade policies, and geopolitical considerations. Monitoring changes in custom duties is crucial for businesses engaged in international trade.

There are several key factors that influence the tariff rates applied to different product categories:

1. Domestic Industry Protection:
   - Governments often impose higher tariffs on goods that compete with domestic industries in order to shield them from foreign competition.
   - The level of tariff protection tends to be greater for industries deemed strategically important or politically sensitive.

2. Revenue Generation:
   - Tariffs provide a reliable source of government revenue, especially for developing countries.
   - Goods with inelastic demand or associated with wealthy consumers may face higher tariff rates to maximize revenue.

3. Trade Negotiation Priorities:
   - In international trade agreements, countries seek to gain favorable tariff rates for their major export industries.
   - Sensitive domestic industries are often protected with higher tariffs during trade negotiations.

4. Geopolitical Considerations:
   - Tariffs can be used as a foreign policy tool, with higher rates applied to goods from adversary countries.
   - Retaliatory tariffs may also be implemented in response to other countries' trade actions.

5. Stage of Economic Development:
   - Developing countries tend to have higher overall tariff rates compared to advanced economies.
   - This allows them to protect infant industries and generate revenue.
   - Developed countries have generally liberalized trade more extensively.

6. Product Characteristics:
   - Goods viewed as luxuries or non-essential may face higher tariff rates.
   - Raw materials and components may have lower tariffs than finished consumer products.
   - Environmental or social impact of a product can also influence tariff levels.

7. Administrative Factors:
   - The complexity of customs procedures and enforcement can impact actual tariff rates.
   - Tariff schedules may be structured to minimize administrative burdens.

Understanding these key influences on tariff-setting is crucial for businesses navigating the dynamic landscape of international trade and customs duties.