Writers of the ''dirty realism'' school (like Ann Beattie and Bobbie Ann Mason) pepper their fiction with the names of so many trademarks and products that critics have sarcastically accused them of getting free samples from the manufacturers they mention. One of the genre's greatest names, the late Raymond Carver, actually pulled off such a stunt, according to a new book about Carver by Sam Halpert, but he played a trick on his benefactors. In an excerpt published in the Paris Review, Berkeley novelist Leonard Michaels says Carver once had simultaneous teaching jobs in Santa Cruz, Calif., and Iowa City, wangling free flights between them on United Airlines by ''telling them he'd put United into his stories. Of course, he never wrote a word about them. He also had a lover in Denver where he changed planes. So there he was, holding on to two teaching jobs, a couple of thousand miles apart, and drinking and carrying on a love affair, and conning United into flying him back and forth.'' Carver later settled down with poet Tess Gallagher, quit drinking, published his 1983 masterpiece, Cathedral, and at the pinnacle of his fame died of cancer in 1988. United spokesman Joe Hoskins says, ''I've never heard of any kind of transaction like that. It's not the kind of thing we do. I'd be suspicious.''