A few years ago in a previous house we had a cat that would pee on the floor instead of it's litter box. We had heard a trick of using a black light to find the exact location (it works). We also used one of the enzyme style stuff to remove the smell.
I think any of the posts in that thread that talk about the smell being in the pad and maybe soaking into the subfloor and wicking up neighboring walls is right on. IMHO I also personally think that most "smell removers" are just perfume that cover the smell and don't do much to remove it. But I could be wrong.
Personally unless the house is already priced in a way that factors in the total replacement of all carpet, padding and potential other work, I would walk away. With the carpet in place you just don't know how extensive the problem is.
Anyone see the recent local report where the lady had all of the cats in the house and the neighbors were complaining about the smell. The urine had soaked through the subfloor on the second floor and was staining the ceiling on the first floor?

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Richard Casto
1972 Porsche 914
2013 Honda Fit Sport
2015 Honda Fit EX
http://motorsport.zyyz.comMoney can't buy happiness, but somehow it's more comfortable to cry in a Porsche than a Kia.