Whenever a petition is filed with the public officer by the Construction Official, the Health Inspector or any other officer in charge of any department of the borough relating to health, fire, building regulations or activities concerning dwellings in the borough, or by at least five residents of the borough, charging that any dwelling or dwellings in the borough are unfit for human habitation, the public officer shall, if preliminary investigation discloses a basis for a charge or charges, issue and cause to be served upon the owner of and the parties in interest in such dwelling or dwellings a complaint stating the charges in that respect and containing a notice that a hearing will be held before the public officer or his designated agent at a place set forth in the notice and at a time that shall not be less than 10 days or more than 30 days after the service of the complaint. A complaint or order issued by a public officer pursuant to this chapter shall be served upon persons either personally or by registered mail, but if the whereabouts of such persons is unknown and cannot be ascertained by the public officer in the exercise of reasonable diligence, and the public officer shall make an affidavit to that effect, then the serving of such complaint or order upon such persons may be made by publishing the same once each week for two successive weeks in a newspaper printed and published in the borough. A copy of such complaint or order shall be posted in a conspicuous place on the premises affected, and a copy shall be recorded or lodged for record with the Clerk of the County of Bergen. The owner and parties in interest shall be given the right to file an answer to the complaint and to appear in person or otherwise and give testimony at the time and place fixed in the complaint. The public officer shall not be bound by the rules of evidence prevailing in courts of law or equity.