Has a 5 year old 40 year roof and a 1 year old 93% efficiency condensing gas boiler.

I have spare sets of agitator dogs, refridgerator circulation fans, gas valves for hot water heaters, etc. 

You should be able to verify the validity of a contractor's license on your State Contractor License Board's website.

In my municipality, I can put the gas and electric entirely in the tenant's name/account, so I'm not liable for that at all.

They normally aren't going on a fishing expedition looking for violations outside of that unless there is a life/safety issue that is obvious in front of them that can't be ignored, like a tenant using the stove for heat or an active leak from a collapsed ceiling.Sometimes the complaint is valid and could cost you, other times its something silly and not a violation.

Insurance, prop tax, mortgage, elec/gas/water if no individual metres, maintenance etc etc I always ask for statements so I can get a rough idea what I will profit.

If you are paying all utilities (electric, gas, and water), then I would expect expenses to be higher. 

Also, if you don't have a valid photo ID of the tenant, can you confirm with 100% certainty that it's the same person named on the lease?

If he has a valid invoice from a company, and no one has photo evidence otherwise, work was performed and the judge may side with him as we would assume a reputable company would not spend 70 hours cleaning an already cleaned unit.

From my understanding the biggest thing holding back commercial development is the availability of utilities (especially natural gas).