This test was devised for groups like doctors, dentists, attorneys, and other professionals who maintain offices in their homes and regularly see patients, clients or customers there.

It doesn't apply to a teacher seeing students at home, because the students are not considered clients or customers. To satisfy this test, patients, clients, or customers must be physically present in your office. Talking with them on a phone from your home is not sufficient.

Note: It's possible to satisfy this test even if the space in question is not the principal place of your business. For example, a lawyer with an office downtown (which is her principal business location) could conceivably satisfy this test by regularly seeing clients in a space at her home in the suburbs.