Take another look at the passage:
To save money on a haircut that he badly needed. Raja let Tina, his roommate and an aspiring stylist, trim his shaggy head. Honestly, a blender or a weed whacker could have done a better job!
You chose the third part, Honestly, a blender or a weed whacker could have done a better job! This part has a main clause: whacker is the subject; could have done is the verb. A fragment will not have a main clause.