Supposedly, no real profit can be made without exploitation. Yes you read right. Profit is only made by paying other people less than the value of what their labour power produced. Sometimes even less than half of what they actually produced for the capitalist.

Means of production and raw materials have value, but they are constant, they do not add any more value to the finished product than the sum of their original value.

Buying low and selling high will give you revenue, earnings, or in short more money but this money is not profit in the capitalist sense.

For an increase in wealth to be considered as real profit, it has to be the fruit of another person's surplus labour, this surplus labour which the capitalist does not pay for as it has been socially accepted that one only gets a fair day's wage for a fair day's work. What the worker in fact gets is just payment for his necessary labour and not for all of his labour. So the fair day's wage isn't so fair after all.

But it is this vital definition that all the arguments that are pro/con capitalism or whatever lies upon. According to Marx all profit is exploitation hence wrong, others will have a different view.

Bottom line is though, if indeed capital (means of production and raw materials) is a constant thing, whose sum of all parts will never be greater than from when it came from originally should no labour be applied to it, how then should we really compute fairly what is to be paid for the said labour that is needed to convert capital into commodities which then will generate profit when exchanged for money?