So, if I have it right - buy some stuff, but don’t pay for it for 180 days… fine. In the meantime, sell it, then with the cash (which presumably is also on 180 days terms, so you borrow the money from the promise to buy), buy some other stuff (on 180 day terms) and sell it (on 180 day terms) a number of times and make a packet. Pay the original purchase. Left over = profit.
The “make a packet” bit is the one that has me worried. If ‘everyone’ is in on this trade, then it means that they are bidding each other up - trading bits of different coloured tulips to each other because the carry is more profitable than the margin cost (or some terms like that…).
Of course, if this type of activity, not to mention massive over-building of shopping malls and new cities were to lead to a bubble in commodity prices, that would be frightening, especially for countries like Australia, Chile, and Canada. Let’s have a look: