Thank you for the suggestions. We are lucky in that we have no carpet in our home. We also do not allow our pets in the living room, dining room, or guest bedroom. The rooms they spend 90% of their time in are the family room, office, our bedroom, and the workshop where their kennels are. All of those rooms other than our bedroom are in the basement.... which is very hard to air out. We painted 3 coats of KILZ and 4 coats of floor paint on the cement floors of the workshop and laundry room, along with repainting the walls in those rooms, and we washed down the walls and other flooring in the finished rooms with bleach water. I guess that I feel that if you are a person who doesn't have pets, that there is NO way you are not going to know that we have pets. We have 3 dogs, 4 cats, 2 hamsters (my sister's who is at college), and 2 large aquariums.
We had a showing yesterday and an open house scheduled for tomorrow, so will see what the feedback from those are. Keeping our fingers crossed that it's better. We are looking at the air purifiers, too, tomorrow. Thinking we can get a few smaller ones, one for each room, like suggested below.