As inspectors we never know what we are getting into. The phone rings, we get scheduled for a given time and arrive expecting the house to be relatively clean. Opening the door to the house the first inhale of air started my gag reflex, so bad that I went back to my vehicle and got a respirator to try and counter the foul stench of a hot dirty closed up house.
At one end of the house, the stench of hardwood flooring impregnated with years of pet urine and on the other end carpeting in the primary bedroom where someone had been incontinent. Old stuff discarded in all the rooms, piles on the furniture and the floor all smelling and looking dirty.
Smells like these can be extremely difficult to completely eradicate. The whole house would have to be stripped down and all floor coverings removed. Then the whole house washed down and sanitized inside. All the floors treated with pet odor neutralizer. If the house is vacant an ozone machine (available from tool rental companies) could be used, they can help lessen or remove odors .
If those methods do not work the sub floor may have to be removed and replaced. If it’s concrete they can be painted with a few coats of polyurethane to seal them.
Unfortunately here are no guarantees when it comes to getting rid of really bad smells from filth, nicotine and particularly urine from male cats that have not been neutered!
NOTE: Do not use bleach on urine, it changes the monocular make up and makes the smell worse.