Maryland attorney  Heather Sunderman at the Maryland Family Law Blog has written a thoughtful piece on locating hidden income in divorce cases:

When the opposing party has a W-2 issued from his or her employer, it is fairly straightforward to determine gross income.  When a person is self-employed (an independent contractor, for example), there can be a huge discrepancy in the amount of income claimed and "real income."   For example, see this article in the Washington Post which describes how prevalent tax cheating is.  In the D.C. Metro area, it is not at all unusual for one or both spouses to be self-employed, perhaps even engaged in several different businesses.  Self-employed individuals may be highly-paid consultants, own a franchise retail business, direct sales, or may provide services such as hair stylists, tutors, and child care to provide just a few examples.  If you may be entitled to child support, spousal support/alimony, attorney’s fees, or a division of marital property, you will want to be sure that the Court has all the relevant information to make a fair decision.  How do you do this?  First of all, try to gather all the information you can.  Who are the clients/contractors/customers of the business?  What assets are owned by the business?  It can be quite complicated, and you will likely need an attorney.  Depositions and subpoenas may be needed, and you may even need a expert or investigator to decipher the information and possibly testify. 

SOURCE: Maryland Family Law Blog