To fly for free is performing work for free which is illegal. Your name will be very quickly known amongst the aviation community and will become mud. Don’t do it.
Pretty much what my old Instructor (the late Tony K) used to say....well more like thundered actually.
"Once you have your Commercial Licence you will never work for nothing..." he would roar on occasion.
He added that for those who did, word generally got around and they found themselves shunned by others.