The folks researching micrometeorites at Glasgow University tend to reject anything that isn’t strictly spherical. They’d expect to find three or four on an area of a football pitch, so almost everything a magnet will pick up from a gutter will NOT be a micrometeorite. If there is any metal working within 30 or so miles, most of the material will be from that, as well as weathered from local building materials.
There’s a Japanese anime (and manga) called “Ruri Rocks” (or “introduction to Mineralogy”) with an episode where the gang go looking for them. They emphasise that there might be one or two meteorites in an awful lot of other (mostly man made) things.