Check what kind of finish you have first.
I have read a method. If you put two drops of water on corner of the floor, the floor surface turns white in 10 min.The floor finish is wax. For wax floor you only need to wax it.
If you use a coin scratch the floor surface, something white came off but not the wood. It is a surface finish. You can lightly resand the surface (not sand to wood) then reapply three coats of Water Based Polyurethane.
Only very worn floor needs to be refinished. You sand it down to the wood, then apply Polyurethane.
An orbit palm sander cost about 50 to 100 dollar. For light sand job, a few dollor sand pad is good for DIY.
