Wood is very porous and will hold that odor for a long, long time...

Happy sellers don't cry foul. 

Have you ever had a tenant argue with you about an odor?

You will do a better job if you are alone and follow a checklist to ensure nothing is missed.You'll also find that a lot of odors can be masked right when they move out.

Don’t know if you’ve ever had a foul up with swing or sizing but if so the lumber yards have a no return policy if it’s not their fault.

Inevitably, animals leave a trace (odor, scratching, and so on).

When this happened in one of my buildings, I went into the complaining neighbor's unit and smelled the odor myself. 

Perhaps I am too small fry (looking for sub 100K loans), don't make enough money, have a personal odor, I don't know and they won't tell me!

There is enough grey area in the IRS rules that often you leave yourself open to an interpretation by an individual IRS agent, rather than by some code your CPA can point to then cry "FOUL!"

No harm no foul