Check the cost of that deep cleaning and make sure they have the means to remove pet dander and make sure they GUARANTEE there work! Then charge at least that amount (plus any down time) as a pet fee.
This is highly important. I recently have read and heard on TV (think it was Dr. Oz but don't qoute me) that cat dander will linger up to 90 days...
CASE IN POINT - A MUST READ: That info brought me back a few years ago when a fellow innkeeper told me he had found evidence of cat in his cottage after the guest had checked out. He did not allow pets. He said he cleaned the place from top to bottom (since cats like to climb, nothing is out of reach). Two months later, and after many other guests and cleanings, a person with a cat alergy checked in. Minutes after entering the cottage her eyes turned beet red, started watering and she ran outside. When he rejoined her she said 'A cat has been in there'....needless to say it was not a pleasent experience for him..
Dander lasts years. Granted, in a confined space it's easier to clean up, but overall an animal in your home for the standard lifespan of a pet, means 2 years before you've gotten it all cleaned up. (Of course these cats are not staying for a lifetime and a lot depends on how clean the cats like to be, the cleaner the cat the worse the dander.)
The whole litter box and spraying thing is why I don't take cats.
BTW, that cat allergy, the previous guest could have been a cat owner. It didn't have to be from so long ago. I find a lot of dog hair and cat hair stuck to guests' suitcases and coats. You know that's all ending up in the room, too.
For all the guests who say they have extreme allergies, don't put them in the dog room, there is no way I can tell pet owners to clean their belongings before they come here and sit in the dining room with Fluffy and Fido all over them. The actual pet would be worse, but the clothing can make me wheeze.