In my experience a good varathane finish will seal the odor in.

If this is really @James Wise you are so foul for the above comment. 

I bought my primary residence with a strong cigarette odor as well.

Bleach only removes color and odor wont kill root structure. 

Some molds are visible and odorous; others are harder to detect.

If there was oil in the basement , the smell would hit you like a ton of bricks , heating oil is diesel fuel , it has a strong odor .

Have any of you found any diffusers or other form of deodorizers to be particularly effective in your STRs that aren’t overpowering or otherwise like a nuclear odor bomb going off like those gyro style twist and open air fresheners?

Odor and aIrborne pathogens are my concern.TIA for any input.

Without the details on cash flow, I can't say you should, just advising to make sure you consider that as an option.Thanks for bringing a foul tip to the completed deal diaries, guessing you've already saved someone else a few grand by sharing lessons learned.

The carpet was completely destroyed by urine and general pet odor.