The contractor should have put down heavy paper protection, which comes in rolls. In future, you might insist on this, or even keep a roll around just in case.
What kind of wood is on that floor? Some woods are softer and more prone to damage. That would be helpful information, but i think it's a matter of the finish, even if it's a fairly soft wood. I'm not an expert on flooring,so I'd likely do a little research on finishes specifically for flooring. Here's a place to start: Which Finish Is Right for Your Hardwood Floors?
What kind of wood is on that floor? Some woods are softer and more prone to damage. That would be helpful information, but i think it's a matter of the finish, even if it's a fairly soft wood. I'm not an expert on flooring,so I'd likely do a little research on finishes specifically for flooring. Here's a place to start: Which Finish Is Right for Your Hardwood Floors?