Don't forget, there is good money to be made restoring wood floors. I'm not talking about cheap Formica laminates but any floor with a genuine wood top layer.
The protective finish on these wears over time and needs replacing before the underlying timber is exposed.
It is not hard to do as you only need to apply a chemical sander to the floor allow to work, mop off, allow to dry and apply finish coat. Rates £20-25 square metre.