"The clamp shelf idea could be saved if they used a pipe-style clamp, though honestly, the teeth on the bar they used could hardly be called "serrated" and would likely not harm any books unless they were particularly heavy. Those clamps are designed to quickly slide when not occupied, so cranking would be minimal. As for divots, they should have added small flat pieces of wood at the contact point. That's how damage to wood is prevented under it's original use."