So in hindsight, I guess it's a good thing that I never bought any of the "systems" they were hocking.

However, you reach a point where you start paying a premium for the installation, as roofers have to use jacks & tethers to stay on the roof.Since a good quality, well installed flat roof system - even those installed 20-years ago - should have had a usable lifespan of 20-years (modern systems, well installed, should be expected to last 30 - 40 years), I would seek a new roofer.  

Anything that constitutes a major inconvenience to the tenant, such that a reasonable court would find one negligent for not addressing quickly, constitutes an urgent maintenance need.Example of the former: leaking water, gas, exposed live electrical wires, smoking in electrical panel, dangerous leaning tree, etc.Example of the latter: poor heat performance of heating system; clogged gutters overflowing causing basement dampness; etc. 

I realised I had a lot to learn and set about reading books, posts and pod casts.

Put in any offer, even if you know it won't be accepted, it will get you used to your systems, and learn negotiating skills for the real deal!

Typical guru always comes back with claims of a room full of attorneys blessing their system or product and denying any unethical or illegal aspects.  

The difficulty really depends upon how the heating system was installed from the get go.  

I wish that I could trust and believe in there system but in the end I have to go with my gut!

Some are more expensive than others (HOA) fees, some have central water and sewers while others have well and septic systems; most all have recreational facilities; you will find a wide range of prices, dues and taxes.  

I use a system for my flooring and types of things that I do to my rentals.