A word that commonly gets thrown around in the Amazon space is replens.
As the name implies, a replen is an item that you're able to replenish over and over again while adding consistent profits to your business.
When making the transition from books to arbitrage, I also strongly believed in this concept.
I've also had several of my coaching clients ask me the best way to find these types of items.
However, over time I've come to the realization that it's not that simple and you can't realistically find items you'll be able to sell forever.
This doesn't mean that every item you buy is a "one and done" type deal, but you need to be smart about restocking items and the risks that are associated with doing so.