Rebecca,
I think you first need to ask yourself these two empirical questions: (1)
Do merchants appear in precapitalism? And, if so, (2) do merchants down
through history, in general, profit from their activities?
If you answered yes to both empirical questions, then you have to ask
yourself this theoretical question: How do merchants do this in a context
other than the ideal-typical industrial relations Marx abstracted from
advanced British capitalism in the mid-1800s?
A related question that may come up in your puzzling over the matter is
this: Whence the source of surplus labor? You will find, I think, that
surplus labor exists down through history; and, further, you will find
that there is surplus labor that exists in the capitalist world market
that does not find its origin in industrial wage-labor. In fact, I bet you
will even find that surplus labor comes from sources where no wages are
paid at all. In the later instances, you will find, I think, that there is
no system of equal exchange between those who appropriate surplus-labor,
and those whose labor is exploited. How is this possible?
The assumption in back of your question implies that profit, and,
moreover, surplus labor, is not possible in a system other than advanced
industrial capitalism in Britain in the mid-19th century where commodities
are on average exchanged for their values, values which are determined by
the amount of wage-labor contained in them. But I think that if you study
the matter you will find that this assumption is false.
If you are asking me how merchant capitalists make profits in the
capitalist system, I can tell you, just as Marx will tell you, they did it
by buying and selling. If you ask me where the value comes from, I can
tell you, just as Marx will tell you, from the exploitation of labor in
various forms, in surplus labor that is bound up in the form of
commodities moving through the capitalist market, of which merchants work
as specialists in the sphere of circulation.
Maybe somebody else can help you, but all I can say at this point is that
you mustn't keep bending reality to pure special theory, but rather you
must theoretically explain empirical reality. Your error is in failing to
apply general Marxian theory flexibly to understanding a historical system
at different stages in its development; putting this another way, your
error is in trying to force a special theory developed about one stage of
capitalist development in a core nation onto other stages of history and
other economic sectors for which this special theory is, at least in part,
inappropriate (at least without modification).
Peace,
Andy