Questionable sources are sources with a poor reputation for checking the facts, or with significant conflicts of interest, such as self-published material, promotional publications, partisan outlets and works produced by the subject itself.
Questionable sources may sometimes be used for simple, uncontroversial facts about their own publishers or subjects, but they should not be relied on for strong claims, and they do not establish notability. Where a claim matters, find a source that meets Bharatpedia:Reliable sources instead.