If your stainless steel pot have yellowish stains inside or outside, do not worry, it is not time to buy new one yet. Before trip to the store you should try to clean it first. I found out that the best way to clean stubborn stain is with glass cook top cleaner, my preferred brand is Cerama Bryte.
Put some cleaner on the pot and clean with scrubbing cloth. Sometimes it is necessarily to repeat procedure. Rinse thoroughly and dry with kitchen towel.
It should restore shine to your pots.