I have genetically yellow teeth and I would like to whiten my teeth. I have tried take home trays which was ineffective. I am now considering KoR whitening deep bleaching system. I found two doctors that perform this treatment in my city. However, one charges 1025$ and the other charges 500$ Should I be weary of the 500-dollar treatment? Why is there such a big gap, since it's the dental hygienist/technician that does the treatment anyways? Also, is there a money back guarantee for the KoR?