Bart,

You need to be delicately honest with the home Owner's.  They know that there is an oder in the basement.  Suggest moving the litter box to the main level of the house where it will not be out of sight out of mind.  Then suggest that they have the basement professionally cleaned and deodorized.  GOOD LUCK!

Unfortunately as their agent it is your job to tell the bitter truth.  Just tell them the biggest turn off to prospective buyers of the property is the odor in the basement.  Hopefully they will take the hint and fix the problem.

Bart,

Good points. Our office pitched in a bought an ozone machine. Park it in an empty home for a few days, and most of the odor is gone. Cat urine is the worst, so you may have to remove some concrete. I'm not kidding. Had to jackhammer out concrete in a listing years back. Good luck!

Hire a home stager to come out. They don't mind being the bad guy and they have so many great things they can do your seller might actually listen to them.

Bring on the full discloser baby! I am the agent that would walk into the basement and say something along the lines "Whoa nelly, we are going to have to see about THAT odor!" Okay, maybe not that blunt - but the truth is going to come out. Do we really assume here that the sellers don't know the smell is there?

It is likely that their noses are conditioned to the smell and they no longer smell it.  Bring in a urine detecting black light and show them the scope of the issue and they will be so disgusted from "seeing" the problem, they will do something about it. Worked for me!  Good carpet cleaning companies usually have this equipment.

For any realtors or homeowners dealing with the odor problem I have found the miracle solution.  I am the property manager to a large apartment community.  At the beginning of every month I deal with odor problems from recently vacated apartments.  Some are more severe than others. Last month we had a really severe smelling apartment.  Even after fresh paint and new carpet we couldn't get cat urine smell out.  One of my maintenance guys brought me a product called Room Shocker this product works like no other product have ever tried.  It's simple to use and not labor or time intensive.  So there's no scrubbing or spring or wiping.  It's relatively inexpensive.  It's not a masking agent and gets rid of the odor at the source.  It not only gets rid of the smell, but it completely Decontaminates and disinfects the whole room.  So far I've been able to get rid of severe pet odor, the smell of cat urine, heavy cigarette smoke odor.   I had trouble finding the product but I found it on a website called BiocideSystems.com.  I guess it's fairly new.  I swear by this stuff now and then highly recommend it to realtors and  Or apartment managers and owners. The stuff really works!

LS