We have had success with either offering these to a tenant or getting them to purchase their own to remedy the smell as the carbon media captures the odor. 

These mats were quite expensive ($40-$50 per piece x 15) and now have a musty odor which we have not been able to removeShould I be concerned?

I have an Ozone generator I use between tenants to kill odors, mold and bugs.

It could have a pet urine odor, mold or musty smell. 

They estimated $98,000 for the job and wrote this, basically saying that it's impossible to fix without also replacing the drywall and insulation, and that chemicals and paint would not be enough:"The odors and residue from the smoking are very apparent and appear to have permeated all areas of the Residence to such a level that these odors and residue, that is oil based, cannot beremoved by means of scrubbing with a detergent solution, application of a deodorizing solution, and application of a stain blocking type paint. 

No fuss, no foul. 

If you don’t like it, no harm no foul.

Their pee has a stronger odor because it is more concentrated than dog pee. 

They will be addressing the flooring, the ac ductwork, dryer vent, and odor removal.

I do a quick filter change and condensation line cleanout every 3 months, main purpose to get in the house to do a general look around for obvious issues like animal and smoke odors.