That's true, but what you will often find is that people play their cards very close to their chest and not really speak about that so they can keep any success quiet and away from others who may then try to horn in on their action.
I can tell you how I started and that was in the second hand market, auctions, garage sales, charity stores, weekend markets and so on. I also bought white goods from local newspaper classifieds and run those on eBay as well. That got me and a friend to a point where we were buying out whole garage sales for a fraction of what they wanted on everything individually and making a killing on eBay.
I guess you would say I'm old skool lol, if I was still in the market, it would be the second hand market still. I'll never understand why more don't get into it to be honest, but everyone just seems to want to sit at home and drop ship now (along with the other 3 million competitors)