There's nothing unethical about "capturing more value than you deliver" (well, assuming I understand you right; I'm interpreting that to mean side A gets say +10EV and side B gets +100EV). In free trade, both sides benefit; that's why they freely chose to trade with each other. It is a myth that one side can unilaterally benefit at the expense of the other side. So if you actually meant "it's unethical if the consumer is coming out of the transaction worse than they came into it", that can't happen under a system of free enterprise. (To the extent that you think it's happening, you are making a value judgement that a certain side is irrational or stupid to perceive a trade to be valuable)
Now, there are absolutely cases where there is unethical profit, but (under my worldview, at least) those are all cases where the state gives a company a special advantage, or literally gives it money. So, the following is unethical:
- bailouts of corporations ("corporate welfare")
- government providing an exclusive monopoly to a given company
- government de-facto forcing someone to buy a product due to coercion
The following is not unethical:
- making a product, offering it freely for whatever price people are willing to pay