If so, how accurate,comprehensive, and of course reliable, are they?

That will give you an overview that may  help you decide.

@Mike Easton I would recommend "THE SELF DIRECTED IRA HANDBOOK" by @Mat Sorensen, which is comprehensive guide for self-directed investors.

@Daren Card  Here's a MA Fair Housing resource: https://www.mass.gov/service-details/overview-of-f...For landlord/tenant laws: http://massrealestatelawblog.com/2009/07/28/massac...https://www.landlordology.com/massachusetts-landlo...Those should get you started.

Although not as comprehensive as MLS, Redfin is the best to look at the Comps. 

For the tenant screening report, it’s comprehensive and free.

I believe I understand the comprehensive due diligence performed once a contract is signed, but what do you look for before?

Systems Overview, that shows how the money grows and systems that make it happen including       Due Diligence and Property Acqusition Systems with Deal Analyzer       Rehab Management systems with sample Repair Estimator, Scope of Works       Exit strategy3.

I see you are a customer, you can also find a good overview on our our support website as well.As for Don's contention about 3 days, you'll find that easily with us or other providers in large counties, but not in the smaller counties unless you want to sit at the recorder yourself, or pay someone to do it.

Its the most comprehensive data-set available and costs about 8 cents per downloaded record.