How do I remove dark pet stains on my finished hardwood floor?

If the stains are more superficial, there are options. Sand off any remaining finish to expose the extent of the stain. This will also expedite the cleaning/bleaching process, as all the wood grain is exposed. It may help to tape off the damaged area to prevent bleaching of the unaffected area. Brush on straight hydrogen peroxide (sometimes called "blond in a bottle") and allow it to dry. Do this multiple times until the stain is gone. Lightly abrade the area and apply stain to match the surrounding areas as close as possible. This works best when sanding the entire floor. After getting the color matched as close as possible, if needed, you can apply thin coats of tinted finish to blend the entire floor and achieve a uniform look. Always clear-coat after applying tinted finish so the color won't "walk off" during use. Simply choosing a dark stain can help disguise stains that won't completely sand out.

I would like to know the answer to this question also. I have the same problem.

Rugs?

Hydrogen Peroxide. Test first for a short time, checking on it now & then. Pour peroxide on the stain & cover with paper towels, getting them really wet. I left it on overnight & whenever the towels & floor were dry I would pour on a little more peroxide. I did it a few times a day until the stain was lightened & not as noticeable.