You can explain to them that everyone will be paying for the water and heat that they use. 

Yup, always a good idea to look at your property and objectively ask yourself "would a reasonable person choose to live here?"

There was a fairly well explained checklist for POF and the other stuff but not a lot of leeway on how anything is done. 

I put a link to a video that explains how to use the biggerpockets rental calculator.https://www.youtube.com/watch?

Is there somewhere that explains that better and what the rules are? 

Weaver  it's a bank or buyers appraisal the objective remains the same, get the highest number.

At the end of the day, if it's a toss-up after he explains WHY it will be difficult to refill the vacancy, you'd better side with him and leave it alone.

When the tenant did finally call to ask about the locks being changed, she explained that her roommate and she had parted on bad terms.This is not over - the owner faces potential issues due to the do-it-yourself eviction (not legal in IL).

I explained it in the optional description but apparently that isn’t displayed anywhere.....

You need to go the tax office and explain what is happening.