By now, with the enormous hype that has been spun around it, there probably isn't an earthworm between John O'Groats and Land's End that hasn't heard about the auction of Damien Hirst's work at Sotheby's on Monday and Tuesday - the special character of the event being that the artist is offering the work directly for sale, not through a dealer. This, of course, is persiflage. Christie's and Sotheby's are now scarcely distinguishable from private dealers anyway: they in effect manage and represent living artists, and the Hirst auction is merely another step in cutting gallery dealers out of the loop.

If there is anything special about this event, it lies in the extreme disproportion between Hirst's expected prices and his actual talent. Hirst is basically a pirate, and his skill is shown by the way in which he has managed to bluff so many art-related people, from museum personnel such as Tate's Nicholas Serota to billionaires in the New York real-estate trade, into giving credence to his originality and the importance of his "ideas". This skill at manipulation is his real success as an artist. He has manoeuvred himself into the sweet spot where wannabe collectors, no matter how dumb (indeed, the dumber the better), feel somehow ignorable without a Hirst or two.

Actually, the presence of a Hirst in a collection is a sure sign of dullness of taste. What serious person could want those collages of dead butterflies, which are nothing more than replays of Victorian decor? What is there to those empty spin paintings, enlarged versions of the pseudo-art made in funfairs? Who can look for long at his silly sub-Bridget Riley spot paintings, or at the pointless imitations of drug bottles on pharmacy shelves? No wonder so many business big-shots go for Hirst: his work is both simple-minded and sensationalist, just the ticket for newbie collectors who are, to put it mildly, connoisseurship-challenged and resonance-free. Where you see Hirsts you will also see Jeff Koons's balloons, Jean-Michel Basquiat's stoned scribbles, Richard Prince's feeble jokes and pin-ups of nurses and, inevitably, scads of really bad, really late Warhols. Such works of art are bound to hang out together, a uniform message from our fin-de-siècle decadence.

Hirst's fatuous religious references don't hurt either. "Beautiful Inside My Head Forever", the sale is titled. One might as well be in Forest Lawn, contemplating a loved one - which, in effect, Hirst's embalmed dumb friends are, bisected though they may be. Consider the Golden Calf in this auction, pickled, with a gold disc on its head and its hoofs made of real gold. For these bozos, gold is religion, Volpone-style. "Good morning to the day; and next, my gold! Open the shrine, that I may see my saint!"

His far-famed shark with its pretentious title, The Physical Impossibility of Death in the Mind of Someone Living, is "nature" for those who have no conception of nature, in whose life nature plays no real part except as a shallow emblem, a still from Jaws. It might have had a little more point if Hirst had caught it himself. But of course he didn't and couldn't; the job was done by a pro fisherman in Australia, and paid for by Charles Saatchi, that untiring patron of the briefly new.

The publicity over the shark created the illusion that danger had somehow been confronted by Hirst, and come swimming into the gallery, gnashing its incisors. Having caught a few large sharks myself off Sydney, Montauk and elsewhere, and seen quite a few more over a lifetime of recreational fishing, I am underwhelmed by the blither and rubbish churned out by critics, publicists and other art-world denizens about Hirst's fish and the existential risks it allegedly symbolises.

One might as well get excited about seeing a dead halibut on a slab in Harrods food hall. Living sharks are among the most beautiful creatures in the world, but the idea that the American hedge fund broker Steve Cohen, out of a hypnotised form of culture-snobbery, would pay an alleged $12m for a third of a tonne of shark, far gone in decay, is so risible that it beggars the imagination. As for the implied danger, it is worth remembering that the number of people recorded as killed by sharks worldwide in 2007 was exactly one. By comparison, a housefly is a ravening murderous beast. Maybe Hirst should pickle one, and throw in a magnifying glass or two.

Of course, $12m would be nothing to Cohen, but the thought of paying that price for a rotten fish is an outright obscenity. And there are plenty more where it came from. For future customers, Hirst has a number of smaller sharks waiting in large refrigerators, and one of them is currently on show in its tank of formalin in New York's Metropolitan Museum of Art. Inert, wretched and wrinkled, and already leaking the telltale juices of its decay, it is a dismal trophy of - what? Nothing beyond the fatuity of art-world greed. The Met should be ashamed. If this is the way America's greatest museum brings itself into line with late modernist decadence, then heaven help it, for the god Neptune will not.

The now famous diamond-encrusted skull, lately unveiled to a gawping art world amid deluges of hype, is a letdown unless you believe the unverifiable claims about its cash value, and are mesmerised by mere bling of rather secondary quality; as a spectacle of transformation and terror, the sugar skulls sold on any Mexican street corner on the Day of the Dead are 10 times as vivid and, as a bonus, raise real issues about death and its relation to religious belief in a way that is genuinely democratic, not just a vicarious spectacle for money groupies such as Hirst and his admirers.

It certainly suggests where Hirst's own cranium is that his latest trick with the skull is to show photos of the thing in London's White Cube gallery, just ordinary photo reproductions made into 100cm x 75cm silkscreen prints and then sprinkled (yay, Tinkerbell, go for it!) with diamond dust, and to charge an outrageous $10,000 each for them. The edition size is 250. You do the maths. But, given the tastes of the collectoriat, he may well get away with this - in the short run. Even if his auction makes the expected tonne of money, it will bid fair to be one of the less interesting cultural events of 2008.