For all the treatment of markets as "natural" I've noticed the particular kind of ethics you mention are very much not natural.

Two places this is evident:

1) It is very, very common for small business owners to be "under-pricing". They price what seems fair & just for what they're doing, which has a tendency to be (sometimes far) under the greed-is-good price that the market could bear. They're often resistant to raising prices on ethical grounds.

2) Children quite consistently have notions about fair pricing that are directly in-line with #1, starting just about as soon as they learn about commerce and tending to persist until someone "corrects" them.

This "natural" feature of capitalism that "can't" be got rid of because it's in our "nature" generally has to be taught.