Any suggestions for removing stains?

Go to or call someone who installs wood floors. Ask them if there is a cleaner that can be used. Don't try anything till you talk to them. Some of these cleaners do not work if another cleaner has been used.

What kind of stains - urine, blood, other? The unfortunate reality is that wood is porous so whatever it is has probably soaked well below the surface and in the seams a large volume of liquid can even soak down to the sub floor. Sometimes the only option is to have it professionally restored or replaced.