Or is getting shellac on any wall at any time helping improve air quality in our unit, and if some smoke gets in while we wait to finish the ceilings, we can just run an air purifier or ozone machine to remove those odors from the unit after we finish the ceilings a few weeks later.

.- After a fire, all studs should either be removed or sprayed with a primer like Kilz to ensure no fire odor.

As for the cat odor I would say your best bet is obviously rip out any flooring and sub flooring and probably 4ft high row of drywall around the entire place. 

You can require a Veterinarians health report on the animal AND require it be annually updated; we require all are spayed or neutered to minimize aggressive behavior and prevent the issues arising from multiple offspring; the animal must be carried by the handler or in a carrier when in confined spaces such as elevators, stairwells laundry rooms etc. unless doing so prevents the animal from performing tasks it was trained for; handler must clean up after the animal in all common areas and prevent offensive odors from emanating from their unit; handler remains responsible for actual damages caused by the animal including cleanup and damage of yard areas; nuisance animals that bark or create other disturbances NOT related to their specific tasks are grounds for removal of the animal and/or the tenant with appropriate notice.Some states do have more or less restrictions within their Fair Housing laws, so you do need to check on that, but our policies have been reviewed and approved by our RE attorneys.

After the first year most lenders do not cry foul if you move and rent out the place.

That odor does not leave.

Well, you can't really do that unless you have a policy in place beforehand stating that applicant odor is a factor.  

Bird excretions have no odor whatsoever!

Over that course of time, both odor and total organic carbon (TOC) levels dropped for all of the pipes.

Perhaps some other solution will be proposed (body odor sniffing technology anyone?)