I would send a lease violation notice that advises the tenant that they have violated the no smoking provision of the lease and that it needs to be cured immediately - to include complying (not smoking) and remove any odor/damage that may have resulted.

One option might be to explore adding air purifiers or filters directly into the system to help mitigate odors.

Ends lease on July 2025.In December, tenant said there was an odor coming from garbage disposal.Tenant had tried their own DIY fixes for a month with no resolution. 

Usually with  a new coat of kiln and paint the odor will go away.

Cat odor is far more problematic than a small dog, but I would check landlord references to confirm how they've maintained their last residence.

Turning on the fan will also help eliminate bathroom odors and odors from harmful bathroom cleaning chemicals.Pro tip: Add cleaning the exhaust fan on your cleaning crew’s checklist during turnover.

If they were smoking outside, the odor would quickly dissipate and would not permeate the building envelope and infuse into the other units. 

Maybe they've been burned by landlords in the past and are being very careful.You can legally reject them based on personality, facial tattoos, body odor, or other factors, but you better make sure you can prove that it wasn't based on any protected class like race, religion, familial status, etc.

The rental had ratty furniture, a record player prominently featured in the marketing but it had no speakers, missing basics items in the kitchen, lots of drunks in the concrete hallways that reverberated right into the bedroom at 2am, a strong odor of urine outside, and more.We have super hosts in this forum that have hundreds of 5-star reviews and are masters of the craft, but I look at their rentals and see they don't have any artwork on the walls, decor is basic, they do nothing to make the guest feel welcome, etc. 

The odors are not always easy to eliminate within the normal apartment turnover routine.