User Activity

So I'm ready to start selling. Well almost. I got a scale, packing supplies, photos of the item, researched what I want to price my items at. Now I'm stuck at shipping. After sifting through a ton of information I'm still lost on what's the best way ...
I notice people say they will exclusively use Amazon to purchase items from now on instead of using EBay. Are these people who only buy new products from actual companies? Are there many used items you can find on Amazon? To me, they are two differen...