Edit: OK, did a bit of research.
Wikipedia uses the phrase “barter model of money” when discussing Say’s Law. What they seem to mean is that money is a thing, like an apple or an orange, and when one pays for something with money, one is bartering. This is in contrast to monetary circuit theory, which says buying something with money involves three parties: the buyer, the seller, and the bank.
I don’t think Say is turning over in his grave about this, because first of all their whole theory seems to be quackery, and second of all Say’s ultimate message is unaffected by monetary circuit theory. To me the two issues seem unrelated.
What wikipedia then offers is another attack on Say’s Law: the hoarding problem.
But there is no “general glut” in Say’s view, since the gluts and shortages cancel out for the economy as a whole. But what if the excess demand is for money, because people are hoarding it? This creates an excess supply for all products, a general glut.
Rothbard says that Say’s reply to this was feeble:
Conceding that sometimes the savings might be hoarded, Say was for once
less than satisfactory. He pointed out correctly that eventually the hoard will
be spent, either on consumption or investment, since after all that is what
money is for. Yet he admitted that he too deplored hoarding.
I presume because that “eventually” might be many years later, and in the meanwhile the economy is in trouble, overproducing.
Rothbard then gives his own answer to the hoarding attack:
And yet, as
Turgot had hinted, hoarded cash balances that reduce spending will have the
same effect as ‘overproduction’ at too high a price: the lower demand will
reduce prices all round, real cash balances will rise, and all markets will
again be cleared.
Which is the heart of all replies to the “general glut” problem. Lower the price enough, and the glut disappears.
I have a feeling that you will better understand the whole topic by reading the first chapter of Rothbard’s Classical Economics, An Austrian Perspective on the Historyof Economic Thought, Volume II. In clear, readable prose, he lays out the whole subject of Say’s Law. Naturally, it’s free in pdf form right here at mises.org:
http://mises.org/books/histofthought2.pdf [Sorry, link thing isn’t working].