tbh, anyone who is actually making a killing selling on amazon isn't going to post it here as he'd be digging his own grave because once people realise it's selling and making good money new sellers will enter the market and start competing with each other for customers. The amount is customers is gonna stay the same and anyone who's done business studies knows what will happen if supply goes up yet demand stays the same.
If i'm selling apples for 50p, and buying them for 25p and they're selling really well why am I gonna tell everyone else so they can put up a stall next to mine and start selling them for 50p too, or even less?
I'm going to sell far fewer apples and probably have to lower my price too when new sellers try and undercut me in order to generate sales.