I used the 7 day crest white strips and they did work. It’s hard to notice at first because you look at your teeth each day so they don’t really look different. Other people will notice though.

a professional cleaning by a hygienist or dentist will greatly improve any whitening product.

if your teeth have plaque and tartar buildup, nothing will work.

also keep in mind that fillings, crowns and veneers will not whiten like natural teeth.

They do work. I used Crest, but for a more dramatic result professional is the way to go.
Crest is inexpensive
professional is run about $300-400, but professional is a bit harsher

a home remedy you can try and it does work is
Peroxide and baking soda it works=%2Frecipes.php&q=teeth+whitener&Search=Search