It happened a couple of years ago, during the chitchat that sometimes takes place among backgammon players in a tournament, that my opponent, who had learned that I was a book reviewer, asked a follow-up question: what was it about my opinion that made it more worthwhile than his?

At the immediate moment of its delivery, all I could register was the insolence. Had my opponent been a carpenter, or a physicist, or a hedge-fund manager, no one would have asked him what made his decisions in his line of work any more worthwhile than anyone else's. (Although I gather that once you know how to cheat, being a hedge-fund manager is in fact a doddle.)

But the question rankles, especially when you look below the line these days and see the invective that can boil beneath what you might have thought was a well-considered or graceful piece of writing. "Everyone's a critic," ran the old line the world-weary author could deliver when faced with some obtuse criticism; now it is, for all practical purposes, true. And it does leave the professional critic wondering, during those long, dark nights when sleep eludes her or him: what is the point of me?

It's a pretty sharp question for me, if I may speak personally. I've been writing about books professionally for 28 years, and it's been my main source of income for 23. There have been periods of my life when it's been my only source of income. (And they will not, should I ever write an autobiography, be recorded in a chapter with the title "The Years of Plenty".)

But now it appears that I am wasting my time and that of other readers, for who needs the opinion of a professional critic when all one has to do is read the opinion of the pseudonymous commenter or Amazon reviewer? "Dull, grim and inpenitrable. [sic] To me it came across a heartless tale [sic], I did not find myself empathising strongly with any of the characters or caring if they succeeded of [sic] failed," said one customer review of Ulysses. Well hats off to her for at least trying; and indeed, as she says later on, the book is not for everyone.

That was a cheap shot, I know, and one could delve into history and find plenty of contemporary professional critics making far more obtuse and malicious judgments about the same book; and there are other, more thoughtful reader reviews of the same book on Amazon I could have picked to suit my purposes, only not as vividly.

It's a question of perceived authority. The whole point of leaving a comment below the line is to advertise the fact that you are not above it, or above yourself, so to speak; a cat may look at a king, and any reader with an internet connection can say what she likes in the space provided. But horses for courses, please. When I look on Tripadvisor to see whether I am going to be staying at Fawlty Towers or not, I consider most people are capable of spotting rats in the serving dishes. But I do not feel the same way about reactions to artistic endeavour. What I want when I read a book review is to find out what someone cleverer than me and better read than me thinks about whatever's being reviewed. There are plenty of such people about: it's why I read the literary pages of the daily and Sunday papers whenever I can. Except, of course, for the Sunday Times, because they gave my book a rotten review. Let it not be said that we critics are incapable of pettiness once we turn gamekeepers and find ourselves on the wrong end of an unfavourable opinion. For, as Martin Amis has pointed out many a time, and all critics have known instinctively from the moment they started out properly, the literary critic has to respond to the work in the same medium as the work being examined: language. You don't paint a review of a painting or express your opinion of a ballet in the international language of dance. But if you're going to say what's wrong with Amis's new novel then you're going to have to use the same tools he uses, and if yours are rusty or cheap or poorly made then you're not going to be in a fair fight.

Not that mine are necessarily the shiniest and sharpest in the box; but they're good enough to keep me in work, touch wood, for all that critics these days feel they're the canaries in the cultural coal-mine (although I think the first canaries started littering the floors of their cages when it became common practice to award stars out of five; the words beneath this little row became reduced to little more than the justification for the number given. Publications that resist this trend should be given some kind of award, really). The best critics are the ones who spot or coin the telling phrase, who have done enough research to know when writers are plagiarising either themselves or someone else (and what the difference is between a rip-off and a knowing reference), or who have reading and frame of vision wide enough to compare like with like, intention with intention, across years or cultures if necessary, and who can either honourably salute or insert the stiletto as appropriate. Most importantly, they should be open to surprise or wonder in the face of the unexpected or new. Sadly, one suspects that someone who thinks "inpenitrable" is a word is not going to have these abilities in any abundance. Which is perhaps unfair, because the question of Ulysses's possible heartlessness that my mocked correspondent raises is one that is proper to raise (refutable, but still proper).

And so I attend, reluctantly, to the question of elitism, which I suspect will be a word cropping up beneath the online version of this article. (Those reading the newspaper version will have to content themselves with writing in ink after the final full stop.) It's what my backgammon opponent was basically accusing me of; but what he meant, I'm pretty sure, unless of course he was just simply being rude, was, "Why don't I get paid to review books, too?" To which the answer is: why don't you have a go? Only start like most do, by sending your stuff straight to the literary editors, instead of fighting for space beneath the line. While we still have literary editors.

• Nicholas Lezard's Bitter Experience Has Taught Me is published by Faber