Here's a recent job we completed in Waco, TX - this floor had multiple pet urine stains and previously tiled areas that needed patching. We repaired all these areas and sanded/refinished the entire house. We have the experience to repair most wood floors in any condition!
This home was built in the 1950's. The floor had been taken care of pretty well, but still had areas that couldn't just be sanded out - i.e. the bad pet urine stains. The only way to rid the floor of these particular stains was to repair the floor, sand the entire area, and refinish to match.
The repair process is fairly straightfoward, with the most difficult part being matching new wood to the old. The only way to get an absolutely EXACT match is to have material from another part of the floor to replace the damaged material with. This usually isn't an option, so we must take great care in selecting the proper species, grade, and region of the country the replacement wood comes from.