Taxation on W-9 income
In general, income that results from a W-9 arrangement is not subject to IRS withholding. Rather, it is the payee's responsibility to claim the income on his or her tax return and to pay any appropriate taxes.
For example, the income you receive from freelance work is generally taxed as self-employment income, which may require the payee to make estimated tax payments throughout the year. On the other hand, dividend income has its own set of tax rates, which are often lower than tax rates assessed on ordinary income.
The exception to the lack of taxes withheld is when the IRS has determined you are subject to backup withholding. This can occur for a few reasons, such as your W-9 containing an improper or incorrect taxpayer identification number. Alternatively, the IRS may notify the payer to start backup withholding on interest or dividends because you have under-reported these items on your income tax return.