What are the requirements for me selling client-based software.

Hi first and foremost thank you for your help in answering my question.  I am in the process of helping my aunt in Europe get a few clients for her software business and I would make a commission on any sale and on any time spent helping her with the software design as well (although less so than selling her service).  I was wondering what exactly I need to do to make sure that I comply with fed/state tax laws.  I would be the intermediary between her company and client here since her software is tailored for each specific customer, so I would have to make invoices and such but I wouldn't be receiving the payment, she would be.  She then would pay me whatever commission I've earned and any payment I receive for helping her with software design or calling up existing clients and such.  Thank you so much for your help.  Sincerely,

Javier Avalos.