I have had books requested of me that included qualifications by the requesting member ( like " Smoke Free home only, etc ) When I recieve the request, I have no way of contacting that member to verify unless I accept their request. Then if they decided they don't want it after all then what?

What you are seeing is a member's "requestor condition".  If you can't meet the condition, you need to turn down the request.  Even if the RC says "I would appreciate it", view it as a request and don't view it as optional.  They would not put it in their RC if the condition wasn't important to them.

If you accept the request and then find you need to cancel the transaction because you can't meet their condition, you will go to the end of the FIFO lineup for that book.  If you turn down the request because you can't meet the requestor condition, you maintain your position in the FIFO lineup.

One of you has to cancel.  IF the book is WL, you should cancel and then decline the RCS when it offers it ot them again.  If the book isn't WL, they should cancel and find someone else ot order the book. 

I don't PM with requestor conditions. If I can't tell by the RC if my book meets it or not then the RCS aren't clear enough and that's the reason I give.  Especially if it's WL because chances are the next person won't have RCS to deal with.  PMing to me just causes trouble. What do you do if they don't respond? Do you mail the book anyway?  If it's WL and you cancel then it'll just offer it to them again.  If it isn't WL and you cancel then you go to the end of the FIFO line and have to wait for all the books that were posted after you to be requested before yours is at the top again. 

If the RCS are vague and they get turned down enough times it should prompt them to rewrite their RCS so they are better understood.

It's an inconvenient aspect of the Requester Condition that, unless they provide contact information like their PBS nickname, there's no way to discuss the terms with them.  The best you can do is err on the side of caution, and if you're not certain you can accommodate their conditions, decline the request. 

One of you has to cancel.  IF the book is WL, you should cancel and then decline the RCS when it offers it ot them again.  If the book isn't WL, they should cancel and find someone else ot order the book.

If she hasn't accepted the request, there's no need to cancel.  All she needs to do is decline the request by saying she can't meet the requestor condition.  That leaves her in the same place in the FIFO lineup.  If she accepts the request and then cancels the transaction, she will go to the end of the FIFO list.  So, it's better not to accept the request in the first place.

What James said "...The best you can do is err on the side of caution, and if you're not certain you can accommodate their conditions, decline the request."

And declining an RC does not put you at the end of the FIFO line, your book will be offered to the next person waiting.

I decline if not sure, or if the RC is vague enough to allow different intepretations.  I've only pm'd one requester.  She had a RC for dust jackets, and this hardback was like a library edition with full color hardcover and no dust jacket (positive, b/c I bought it new).  I let her know, she approved, and the transaction went smoothly...but at the time it wasn't like she could wait for the next copy with a DJ, it didn't exist for this book.