Shellac seals in the odors on wood. 

Actual Repairs ended up at $60K ( including some sub floor issues, attic insulation that the buyers negotiated in the DD period with me and pet odor remediation which was harder than I expected it to be !!)

Plus one on the ozone machine for mitigating odors.

X who puts her nose 1 inch from the doorknob and smells it, then proclaims the whole house smells like smoke is very different than a true permeating odor of smoke throughout the unit.Having others come over and smell for it will give you (some kind of) an idea if it need to be abated (or not).Offering to let them out of the lease before move in (if turned down) seems to nullify the need to (try to) abate the smoke smell.

I called her to inform her that my neighbors from downstairs are smoking and the odor is going upstairs (to my apartment) and she rejected my call.

Other items being odor removal, illegal tapping into power, and out if code re-routing of plumbing.

I'd only have them cleaned for the following reasons:MoldPet OdorSmoke Odor

@Whitney Robert Caldwell Hello Whitney, although I have personally not purchased any properties that have had a heavy smoke odor I have heard from others that getting a company to do a thorough duct cleaning can also help.

A gas leak isn't a huge deal unless it is a very strong odor of gas and is making its way around the whole house. 

Also, does these drip fields cause any adverse effect like odor, etc?