(Emphasizing what dascpa said) this should call for a CYA disclosure if you decide to prepare the activity as a business.  Disclosure being that your decision to prepare it this way is based on evidence and argument the client provided to you.  If audited and the IRS overturned the business treatment, your P&I coverage (I'm assuming that's a component of your service) is not applicable in these situations.  Disclosure ie informing the client in writing of course!