The place does have an odor.

Moved in after getting rid of the cat odor. 

No inside access, but it was described as "a hoarding".I spoke with one neighbor who has been inside, she told me there wereintense odors, overwhelming stockpiles of clutter, animal feces, bugs, even rats. 

You can clean the walls with TSP, use an ozone machine (not exactly necessary, but work well to remove odors), use a good oil based primer like BIN or Kilz, and then paint the walls at that point.

Some Kilz odor blocking primer, a coat of paint and LVP throughout.  100k profit!

A tenant just moved out of my rental property and there is a urine odor throughout the first floor. 

I care about my properties and having less damage, and no forever odors.

Meaning, how do we prove there was an overwhelming odor that we had to address in order to re-rent the house?

The odor of cat urine remains.

While you have the right to run a rental, they have the right to grumble about it, and make sure you follow every single rule in the ordinance to the letter.