Depending how long the previous tenant was there, replace carbons/smokes, furnace filter and (maybe) furnace cleaning, fire extinguisher, touch up paint/nail holes, fireplace cleaning (if applicable), dryer vent clean-out, if it's an older property possibly do a roto-rooter service of the main line.

Seems like the biggest risk is that she would fail to hear the smoke detector. 

I don't know how hot your market is, or how smoking of a deal this was, but a guaranteed 10k payday with no risk isn't exactly something to completely ignore.

We replaced ugly dark brown diagonal cedar siding w/ light gray vinyl siding.

Everyone is safe fortunately.The other side of the duplex did not have any damage aside from smoke entering their property. the fire department said they are clear to stay.I have filed a claim with my insurance and am going to get the fire department report tomorrow.

the dark grout lines look great against the lighter tile and should show much better and require a bit less maintenance come turn time.And finally work continues on the hallway, lots of Mud to combat 30+ years of move ins and outs, ceilings have been re-textured and painted. 

They might have parties, or smoke inside, which all could damage the property.

Does anyone have any recommendations for detecting and proving violations of no smoking rules?

Cat and dog odors are more difficult to resolve than smoke from a fire because we understand how smoke from a fire travels inside all the items mentioned above and we don't realize that cat and dog odors travel through the air the same way.We remove everything that can be removed from inside a house as mentioned above, wash everything carefully so we don't allow what we are washing to spread, vacuum walls, ceilings, floors and everything with a Hepa filter in the vacuum, paint everything, clean the air with an air scrubber and the odor still remains very slightly until after someone actually moves into the rental unit.

I wouldn't let the smell of smoke detract you from a deal.