Let's assume that Mars has an atmosphere, oceans, plants, and animals, even there is some native civilization like John Carter.
Is there any possible trading between Earth and Mars?
I noticed that many people like to compare space travel with geographical discoveries (15th-17th century), but this seem not to be a reasonable analogy.
Remember that space is not an ocean, it is almost empty. In order to push a rocket forward, you must bring and consume some mass to accelerate away. Such mass is called working mass. I know that there are gravitation fields, magnetic fields, electromagnetic waves, solar wind, and solar radiation in space, but these are not effective spacecraft propulsion in current technology.
Transporting gold from Americas to Europe does not consume any resources.
PS: This question is different from the question What goods would be worth trading between Earth and Mars?, in which assuming that I've got technology several centuries more advanced than what we have now.