Value added tax (VAT) in theory avoids the cascade effect of sales tax by taxing only the value added at each stage of production. For this reason, throughout the world, VAT has been gaining favour over traditional sales taxes. In principle, VAT applies to all provisions of goods and services. VAT is assessed and collected on the value of goods or services that have been provided every time there is a transaction (sale/purchase). The seller charges VAT to the buyer, and the seller pays this VAT to the government. If, however, the purchaser is not an end user, but the goods or services purchased are costs to its business, the tax it has paid for such purchases can be deducted from the tax it charges to its customers. The government only receives the difference; in other words, it is paid tax on the gross margin of each transaction, by each participant in the sales chain. In many developing countries such as India, sales tax/VAT are key revenue sources as high unemployment and low per capita income render other income sources inadequate. However, there is strong opposition to this by many sub-national governments as it leads to an overall reduction in the revenue they collect as well as a loss of some autonomy. In theory sales tax is normally charged on end users (consumers). The VAT mechanism means that the end-user tax is the same as it would be with a sales tax. The main difference is the extra accounting required by those in the middle of the supply chain; this disadvantage of VAT is balanced by application of the same tax to each member of the production chain regardless of its position in it and the position of its customers, reducing the effort required to check and certify their status. When the VAT system has few, if any, exemptions such as with GST in New Zealand, payment of VAT is even simpler.