If you mean how do you find out how much someone reported as taxable income on their return:
Barring someone that has been provided that information like a loan officer or such, you can't. It is against the law and agreements in most all information requests by outside parties, for anyone involved with a return or it's handling to disclose any information about it.
That even includes IRS employees, who CANNOT even access someones files without an authorization process and reason, and a record being made they did. If the information becomes known, the authorities would pursue how it was discovered.
I believe it falls not just under an invasion of privacy, but as none of your business!
If someones disposable income increases, they are more likely to ride in the comfort of their personal cars rather than make use of the cheaper alternative of public transport. Which will lead to an increase in traffic congestion.
personal income tax
someones personal feelings about sexism
Personal Income = Disposable Income + Personal Savings
Maybe a Good option would be to check if the person is a member of "facebook" or "twitter".
To mow someones lawn for money
No, the typical amount allowed is 25% of disposable income.
individual income taxes
By adding all of your different types of income that you receive, find, work for, provide services for, etc. together to come up with your total gross personal income for the hour for the day or for the year before income taxes.
Personal income is equal to the money an individual makes in a year. Personal income is usually derived from jobs or investments.
Try googling the person you want to find. People tend to include their mobile numbers on their personal pages, facebook, linkedin etc...
Discretionary income, not personal income or disposable income, would be the greatest interest to marketers.