If you got a report that someone was smoking cigarettes or cigars outside only, per the rules, would you post the same question?

I would mention to Tenant B that I was visiting Tenant A and smelled what seemed like marijuana smoke coming from their side and remind them there is no smoking permitted inside the house.

Smoking cigarettes is also quite legal, and also prohibited under the lease.I think your argument on unit count is a red herring here. 

Often I can smell scents from the lower unit that aren't pleasant (cooking, smoking, etc).

Security Deposit: 2600Lease states no smoking/painting walls/no hanging things on wallsTenants have moved out and have left two truck loads of garbage to be removed.Damaged doorPainted walls which got on the ceiling and trim Lots of holes on the walls throughout the houseDamage from windows being left open constantly Weed was clearly smoked in the house (smell throughout the place) so we need to deep cleanWater bill wasn't paid so I had to turn back on utilityMissing keyQuoted costs:$450 junk removal (some furniture)$935 for damaged doors/windows, painting cleaning$30 for utility turn onTenants were only there for a year before moving out so a lot of this is beyond normal wear and tear. 

Depending on the severity of smoke damage and structural issues, it could be a huge challenge for first time flip.

While I use it primarily for noise concerns (it alerts me for sustained +80 decibels), it's also handy for cigarette smoke and tracking temperatures (in addition to our Ecobee thermostat)- sensors on all exterior doors and possibly windows (which you might have via smart locks for the doors)- exterior camsA recent guest for reasons only known to them set the thermostat to cool and 60F in the winter (where it's currently a balmy 11F). 

Like a tornado with a firebomb.....Holy Smokes!

(Ok I get it that its 2024 and people smoke weed).

Smoke detectors are two screws and a batteryScreen door could be tricky depends on if screen just needs repaired or replaced.