Hello llundquest,
If the smell is coming from cat urine odors that have not been cleaned correctly or have not been cleaned immediately and left to sit too long, the odors are very hard to remove completely. Sometimes it will require the removal of the carpet and carpet padding. If this is your dream home, maybe you can negotiate for new carpets or the price to be reduced to allow you to install new carpeting prior to moving in.
Another thing to think about with pets urinating in the house is not only can it damage the carpet and carpet pad but the sub-flooring as well. When pet urine has reached the sub-floor, it will need to be treated with Kilz prior to new padding and carpets being laid to eliminate the odor. Kilz will help to lock away the bad odors.
Here is one of our pages that addresses pet odor removal:
Pet Stain and Odor RemovalWhite Vinegar and Water:For painted walls, you can make a mixture of 1 cup vinegar to 1 gallon water and wash the walls down, keeping the wash rag clean and changing the water as needed. Vinegar is a natural deodorizer and any smell from the vinegar will dissipate shortly. If the walls are bad you may want to repaint again using Kilz before the final color.
Good luck with your search.
Mrs. Clean