Then have them restore it they way it was using a licensed contractor or accept it they way it is.If it doesn't meet code you can have them pay a licensed contractor to make it to code or have them restore it immediately to the way it was.A tenant that takes care of the house and pays market rent on time is worth trying to keep.So get it inspected and then decide which way to go.I'd let them know you are going to step up inpections.

He finds old buildings and restores them to rent out to offices, retail and residential.

Restoration companies are also a good source.

We have a friend (who just sold their restored farmhouse on 30 acres) who had to dig out & install a retaining (fiber-cloth covered) trench for $4500 that has absolutely no function except it's NOW code for all septics systems.The sale triggered the town insisting on the upgrade.

Background on me: I restore classic cars / hot rods full time and do real estate in my off time.

From there I had a few years where I owned a residential custom remodeling company which eventually transitioned more towards insurance restoration work.

@Nick Scapellati  Check out your local Habitat for Humanity Restore as they often have items you can buy for a really good price. 

By now, I feel you don't just deserve to have your property restored to you. 

There is something here called the Habitat for Humanity ReStore.  

Depending on what the smell actually is, I use kilz restore primer and then paint the place.