households?  A lot of my books are from friends or used book stores and I don't know the history of them so even though MY household is smoke free, I can't guarantee that the book has never been around a smoker. 

It seems that even though I cancel the request the same person will request it again.  Maybe I am doing something wrong.

Any help will be appreciated.

No there is no auto-screening.

If people have special requests around non-smoking books, they wil create a "Requestor Condition" that will state their preference.

Many people word this EXACTLY how they want it:

for example "no books from a currently smoking household" means 'Send it if YOU (and your family) don't smoke, I don't care about the history of the book"

other people will say things like "no books that smell of smoke" or "I am highly allergic to smoke" or "no books which have been around smokers", and these types of requests you can decline if you aren't sure of the history of the books.

Also, it sounds like you are getting the same request over and over from the same person with the same RCs? If this is the case, make sure you are declining the book by clicking on "Does Not Meet Conditions" rather than "cannot mail"

you could add a public header to your bookshelf using the button near the top left on your bookshelf to state what you want.  People getting the request from a wish list won't see it, but if they are ordering directly from your shelf they will.

It wouldn't stop all, but it might help.