The law is quite clear about an advertiser’s liability.
https://fairhousing.com/legal-research/hud-resources/adverti...
Section 804(c) of the Act prohibits the making, printing and publishing of advertisements which state a preference, limitation or discrimination on the basis of race, color, religion, sex, handicap, familial status, or national origin. The prohibition applies to publishers, such as newspapers and directories, as well as to persons and entities who place real estate advertisements. It also applies to advertisements where the underlying property may be exempt from the provisions of the Act, but where the advertisement itself violates the Act. See 42 U.S.C. 3603 (b).
Publishers and advertisers are responsible under the Act for making, printing, or publishing an advertisement that violates the Act on its face. Thus, they should not publish or cause to be published an advertisement that on its face expresses a preference, limitation or discrimination on the basis of race, color, religion, sex, handicap, familial status, or national origin. To the extent that either the Advertising Guidelines or the case law do not state that particular terms or phrases (or closely comparable terms) may violate the Act, a publisher is not liable under the Act for advertisements which, in the context of the usage in a particular advertisement, might indicate a preference, limitation or discrimination, but where such a preference is not readily apparent to an ordinary reader. Therefore, complaints will not be accepted against publishers concerning advertisements where the language might or might not be viewed as being used in a discriminatory context.
As far as roommates....
For example, Intake staff should not accept a complaint against a newspaper for running an advertisement which includes the phrase female roommate wanted because the advertisement does not indicate whether the requirements for the shared living exception have been met. Publishers can rely on the representations of the individual placing the ad that shared living arrangements apply to the property in question. Persons placing such advertisements, however, are responsible for satisfying the conditions for the exemption. Thus, an ad for a female roommate could result in liability for the person placing the ad if the housing being advertised is actually a separate dwelling unit without shared living spaces. See 24 CFR 109.20.