The first thing to consider if you want a stain and scratch free sink, is prevention. The best way to deal with a problem is to prevent it from happening in the first place, right?
After each meal, I find food scraps floating around the sink left from food prep and waste being dumped inside or rinsed off from the plates. I’ve found that leaving them to sit for hours will increase my chances that they will stain the bottom.
Even if you don’t do all the dishes right away after each meal, taking a few seconds to spray down and rinse away the leftover grub sitting on the sink will keep it looking nice all day long and do wonders for preventing stains.
Next to my nightly ritual of having a soothing cup of herbal tea, I make it a point to remove the metal rack inside the sink, and give it a quick scrub down with a rag and a bit of dish soap.