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.
In my experience, small businesses often charge more than larger businesses, perhaps because they don't benefit from an economy of scale or increased negotiating leverage with suppliers. For example, compare Wal-Mart to a small general store or Home Depot to a small hardware store. It's much more common that the big box stores charge less for the same products.
Also, from what I remember of microeconomics, the free market model assumes a number of things that are not always true in reality, at least not all at the same time: robust competition among suppliers, perfect knowledge among consumers, rational decision-making behavior. Like any model, the more reality differs from the assumptions, the worse the model is at prediction, but the basic laws of supply and demand, where the price of a good is where the supply and demand curves meet, still hold.
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.