Andrew is of the opinion that nothing in Marx's theory implies that
values of commodities are good predictors of market prices. This
seems to be an over sophisticated reading of Marx, that cedes
too much ground to bourgeois critics of the labour theory of
value. Whilst Marx certainly allowed, like the classical
economists, that market prices might fluctuate around their
values, he certainly indicated that he thought that values
were very good predictors of market prices.
'What then is the relation between value and market prices,
or between natural prices and market prices? You all know
that the market price is the same for all commodities of the
same kind, however the conditions of production may differ
for the individual producers. The market price espresses
only the average amount of social labour necessary under
average conditions of production, to supply the market with
a certain mass of a certain article.'
.... It suffices to say that if supply and demand equilibrate
each other, the market prices of commodities will correspond
with their natural prices, that is to say with their values,
as determined by the relative quantities of labour required
for their production. But supply and demand must constantly
tend to equilibrate each other, although they do so only by
compensating one fluctuation by another, a rise by a fall
and vice versa. If instead of considering only the daily
fluctuations you analyse the movement of market prices for
longer periods as Mr Tooke, for example has done in his
History of Prices, you will find that the fluctuations of
market prices, their deviations from values, their ups
and downs paralyse and compensate for each other; so that
all descriptions of commodities are, on the average, sold
at their values or natural prices....
If then, speaking broadly, and embracing somewhat longer
periods, all descriptions of commodities sell at their
respective values, it is nonsense to suppose that profit,
not in individual cases, but that the constant and usual
profits of different trades springs from the surcharging
the prices of commodities, or selling them at a price
above their value.'
The above quotes are from section 6 of wages prices and profits.
This indicates that Marx held that values were very good
predictors of prices, and it was for this reason that
his theory of surplus value made sense. I see no reason
why we should be so appologetic about Marx's support for
the labour theory of value as an effective theory predicting
what actually happens to market prices.