There exists no agreed general, scientific definition or theory of economic opportunism; the literature usually considers only specific cases and contexts.
[2] Adam Smith famously wrote in The Wealth of Nations that: "By preferring the support of domestic to that of foreign industry, [every individual] intends only his own security; and by directing that industry in such a manner as its produce may be of the greatest value, he intends only his own gain, and he is in this, as in many other cases, led by an invisible hand to promote an end which was no part of his intention.
Adam Smith does not rule out that possibility, acknowledging implicitly that the self-interest and the interest of society may not always be compatible, only “frequently”.
Opportunism could then be thought of as an aberration, a "market imperfection" or a “gray area” that sometimes occurs in normal trading activity.
Nevertheless, the gains or benefits of trading activity (and indeed the losses), although entirely legal, might be distributed very unequally or in ways not anticipated by previous understandings, and thus accusations of “economic opportunism” can arise nevertheless in many different settings.
"[10] Some years later, he explained that "Today’s banks represent the incarnation of profit-seeking behavior taken to its logical limits, in which the only question asked by senior staff is not what is their duty or their responsibility, but what can they get away with.
[12] This creates the possibility that, even though — strictly speaking, or formally – everything is done “within the law”, economic actors nevertheless do not (or not fully) honor their trading obligations in some way, for selfish motives, and therefore commit what amounts to deceit, trickery or cheating, by utilizing a somewhat different “interpretation”, “intention”, “expectation” or “understanding”.
It occurs in trading activities, especially where rules and sanctions are lacking, and where the opportunist actor has great power to influence an outcome by the attitude he assumes in practice.