Is It Worth Being Concerned About Positive-Sum Transactions?

Even if positive-sum transactions are the norm in typically free commercial societies, is it still worth being concerned about? Is it morally problematic that people might be mistaken in systematic ways about what is going to benefit them? Even if they believe in advance, they will benefit maybe they won't or is it problematic that people don't necessarily benefit equally when they engage in these kinds of exchanges? There could be lots of things to be worried about.