"Realtors work for tips"
No offense taken....But let me add a few points:
A Realtor is a member of the National Association of Realtors, which adheres to a detailed Code of Ethics. "Realtor" is a trademark, and should not be used to identify those that are NOT members.
There are MANY, licensed Real Estate Agents and Brokers that are NOT Realtors.
As with many Professions, there are different areas of expertise that still fall generically into the Real Estate Profession. There are appraisers, commercial property specialists, industrial, agricultural, etc. and no one can be expected to have answers to questions in all the different areas. MOST agents just deal with residential. A high percentage of those are probably only "part-time" agents. Some of these part timers are very good for their specific niche market, but as an investor, your needs can not be met by the average real estate agent if you are doing anything other than flipping fixer uppers to retail.
For any other type of investing, and certainly for long term holding strategies, you need to find someone that knows THAT niche inside and out. The only way to gain that knowledge, is through years of hands on experience. There is no one book, or one source, other than an experienced professional, that can begin to provide enough localized information to enable you to make informed decisions.
Expecting that all "Real Estate Professionals" should be able to properly advise you regarding investment property is like expecting all Doctors to be able to perform heart surgery, or all accountants to know the intricacies of the tax code.