Are General Power of Attorney papers worthless?

I am General Power of Attoney for my 86 year old father who has the start of Alzheimers Ampicillin Online Disease. My father signed a real estate contract to sell his house. The real estate agent told me that the power of attorney paper is basically worthless that my father can do what ever he wants and I have no say in the matter. Is this true? Should my next step be talking to an attorney?