[DesertRatTom]

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?

 

[DesertRatTom]

I think I'd try a little sandpaper on an out of the way spot to determine the actual color of the wood. If it's had a deep stain, you'll almost certainly have to have it sanded down to the wood, then refinished. That is a very nasty job, and I'd likely have it done rather than deal with all that sawdust. Then you can refinish. You might also consider trying a few finish removing chemicals in an out of the way spot. Could be that's enough. If it was shiny when you bought it, the owner may have just did a quickie coat with something cheap. When I sold a condo, the agent suggested putting some sort of coating on the worn spots on the cabinets. Looked great, but I bet it didn't last.

I think you're right about the finish being fragile, so after you test and find a remover that works, remove the coating and buy some premium finish. Clean the floor thoroughly first,of course.