In short, online arbitrage is the process of finding products cheap from a retailer & reselling them for a profit on Amazon.
Amazon customers don't tend to shop around, preferring the convenience & reliability that Amazon offers to them. This is where your opportunity lays.
Just by being an informed "middle-man" you can identify these products & grow your business by reselling them.
You make money on the difference between the item from the retailer vs Amazon's higher price.
The hardest part is finding the products in the first place, which is where we come in...