Brought cat to groomer, got her back with bald patches around neck, wtf?

They said she either has flea or thyroid problems and that it just started to fall out when they washed her. She doesn't have flea problems and she doesn't seem ill. We washed her two weeks ago and she had no hair loss. We brush her regularly and she doesn't lose any more hair than you would expect her to shed. There are big and small patches of completely bare pink skin in the neck area. Should we demand our money back or what?