On a recent afternoon at the Brooklyn Flea in Fort Greene, Jake Spetalieri, the proprietor of Catskill Coydog Vintage furniture, was offering a few rainy day specials, including a blue nubby vinyl-covered late 1960s settee for $345 (normally $450) and a sleek, surfboard-shaped white-topped coffee table for $250 ($100 off). The sky was threatening to open any minute, but a …