And while no one has been identified with certainty as the source of the calls, citizen investigators have pieced together enough scraps of information to draw the outline of a money-making racket by home-improvement scamsters.
On the morning of the last big snowstorm in February, Joseph Choi spotted two city building inspectors on his block, 156th Street in Flushing, talking to a neighbor.
“Everyone thought they were coming about shoveling the sidewalk, and it was still coming down hard,” Mr. Choi said. But it turned out the inspectors were checking a report made to the 311 line that the owners of the house had illegally turned a basement into an apartment.
The following week, the inspectors were back, knocking on more doors, rattling more nerves.