Actual
business related expenses are tax deductible. That includes our services for their business. They pay you for doing business tasks and projects, they can deduct your fees. It would be no different than when they hire an accountant, bookkeeper, or office cleaning service, or pay building rent, utilities, supplies, or anything else that is
strictly related to their business. It is deductible.
Take for example if they wanted you to do some personal tasks, such as managing their personal email or balancing their checkbook. Then it is NOT deductible.
This might help to get you started:
http://www.irs.gov/publications/p535/ch01.html
"What Can I Deduct?
To be deductible, a business expense must be both ordinary and necessary. An ordinary expense is one that is common and accepted in your industry. A necessary expense is one that is helpful and appropriate for your trade or business. An expense does not have to be indispensable to be considered necessary."
There are other publications listed at the above link that you can download or view that might be useful.
Hope that helps a bit,