Halacha allows for certain rumors to be reckoned with, but never are they to be accepted as fact.
It is important to note the halachik qualifications which distinguish a rumor that may have some credence from that which is mere character assassination. If the subject is known to have enemies in the community who are very possibly the source of the rumors, it may not be granted any legitimacy. Even if everyone in the community has a favorable opinion of the subject, the rumor would have to circulate throughout the community for one and a half days without losing strength before it could be taken seriously.
When a rumor does seem to have validity, halacha allows for it to cast doubt on the status of the person(s) involved; e.g. where the report concerns the subject’s status as a kohen or similar issues of lineage.
The unfortunate reality is that rarely is a rumor anything more than wide-scale loshon hora. Even when halacha grants a rumor some degree of validity, it cannot be accepted as fact.