Making Millions with Affiliate Marketing

I met with a guy yesterday who is the digitial advertising business and works for one of the TOP online conglomerates around.
He manages the digital advertising of some of the most expensive online ads and websites.
We discussed one of his clients.  He told me that this client nets around $500,000 a MONTH purely from affiliate marketing!!!
His client has no inventory, has no brick and mortar shop and nothing to sell. 
The way it works is:
He is an affiliate of other companies. 
For example: A company has a website that sells expensive jewelry.
An affiliate signs up with that company as an affiliate.
The affiliate invests money in paid advertising in the best positions on the web.
(This is the only expenditure of the affiliate)
Once the ad is clicked on, the customer is directed to the main website, in this case, the jewelry site.
If the customer decides to buy a product, a nice commission is sent to the affiliate.
There is a third party software that manages the amounts of clicks that are brought in through the affiliate's advertising.
So wise affiliates know 2 things:
1) Which e-commerce websites are the most in demand and pay highest affililate commissions.
2) Where to spend their money in advertising.