Knowing if you have sanded too much can be determined by a few key indicators. One clear sign is if the floorboards appear noticeably thinner or show signs of excessive wear. Additionally, if you notice deep gouges, unevenness, or dips in the floor surface, it could be an indication of over-sanding. Another sign is if you can see the nails or fasteners on the surface of the floorboards, which suggests that too much material has been removed. It's essential to regularly inspect the floor during the sanding process and take breaks to evaluate the progress. If you suspect you have sanded too much, it's advisable to consult a professional or a knowledgeable expert to assess the situation and determine the best course of action for achieving the desired result.