but don't worry, it's safely locked down.2) Smell-- figure out the cause, is it a horrible smoker,  bad carpet, or mold? 

Does it make a difference if I put smokers upstairs and non-smokers downstairs.

No smokers!  

I try to employ strict screening criteria for applicants, including verified income 3x over rent, two positive landlord references, satisfactory credit situation (score above ~600 with no negative patterns established), no smokers, and no large dogs.

---------RENTAL CRITERIAGENERAL REQUIREMENTS1.Each adult (18 years or older) must complete an application to rent and background check authorization form.2.Each applicant must provide a valid government issued picture ID at time of application. 3.Each applicant must qualify individually or together with a co-applicant as a household. 4.An application fee of$40 per application must be paid prior to processing the application.5.Occupancy is based on the number of bedrooms per unit.Maximum occupancy is two persons per bedroom.6.No Pets - no pets allowed on the premises.7.No Smoking - no smoking allowed on the premises.We will not rent to smokers.8.No Drugs - no illegal drugs are allowed on the premises.We will not rent to illegal drug users.9.No Firearms - firearms are not allowed openly on the premises.If a firearm is owned, it must be safely stored.10.We conduct full background checks.

She's a smoker and that bugs neighbors.

(missing smoke detectors is one reason why I hate smokers!)

The unit isn’t very nice, she’s a smoker and there’s nicotine on the walls so I can’t even slap some paint on the walls to make improvements.

These days there are plenty of non-smokers looking to rent.

Do they smell like a smoker or try to hide a pack of cigarettes, even though they told me during the telephone interview that they do not smoke?