The phrase "to earn a profit" means to make more money than what was invested or spent. It indicates that the total amount of income generated is higher than the expenses incurred. Full definition
This allows them to advertise for free and yet still earn the profit of selling the actual item. (rentersinsurance.net)
On top of that, local author events at your library or bookstore allow you to give something back to the community (your book) while still earning a profit from sales. (lulu.com)
It is a global worldwide system of buying and selling capabilities of earning profits on the exchange rates. (forex21.com)