@Jennifer1351 ,
unfortunately there are always some disrespectful guests. From my experience they are overall a very small percentage but still it happens here and there - and these guest are not necessarily booking your lodging due to you have instant booking turned on (with instant booking they need to have only good references, otherwise they wouldn't be able to book staight away).
I have three apartments in the ground floor of my farm house where I live in the first floor. For 2 apartments I hav IB turned on, for the third apt I have it turned off, and I live in a very touristic place with a lot of competition. Also I changed a couple of times between IB turned off and on. At the end I don't see a big difference beween teh guest which came with IB or where I had a lot of conversation before the booking. On the other side I believe that there are a little bit more bookings for the apartments with IB turned on than for the other apt without IB, but it might be also due to the fact that my third apt is a bit more expensive because it has a private terrace and 2 bath rooms, who knows...!
I personnally don't think, that you get "better" guests when you turn off IB, but you may feel safer for your own, because you have the possibility to get a fist impression of the guest through the answers to your qeustions. Please note this is no guarentee.
Regarding the smell of smoke I would mention it towards the current guest, may be in a friendly manner "by the way, I always do smell a bit of smoke when I am passing your floor, just wanted to make sure that you are not smoking inside the apartment".
After they left I would proceed according @Branka-and-Silvia0 's tips. If it doesn't help and it still smells smoky, then I would wash the curtains (if any) and clean all sofas, carpets and similar with a wiping cloth which is moist with a bit of vinaigre (not really wet, just a bit of water and a small bit of vinaigre). You will see, this will help.