When a stainless steel pot comes from the factory, the inside is usually highly polished. So much so that it's more non-stick than a non-stick coating. If, from the start, we can stop it from getting scratched, it can act like a non-stick for decades. But anything harder than a fingernail (like metal) or adding salt to a cold pan can cause scratches and pits that rough up the surface and trap foodstuff (and smells) and also make the pot harder to wash.
You can buy specific stainless steel polish and this works marvellously well at restoring the inside of a pot (I use it for high-quality second-hand pots). But it's expensive and the chemicals make my skin try to fall off a bit. For mild scratches, a paste of baking soda and
water, scrubbed in the bottom until the arm is too tired, once a day until it's better does the trick. I
think this would also get rid of the chemicals as it would reduce the micro scratches it can hide.
Scrub buds (plastic and metal), as well as abrasive sponges, seem to scratch the pans very easily in their eagerness to get the food off.