Although a few years ago South Fork dealers were mostly scarce at Art Miami, this year the four galleries that particpated were some of the busiest booths at the fair. For the past two years, Art Miami has held a sister fair in Southampton in July and galleries here appear to like the company's formula for selling art in a cool tent under a blazing sun. Mark Borghi, whose Bridgehampton gallery sells modern and contemporary masters, primarily in the secondary market, said his sales were brisk.