Cabinets, countertops, appliances, clean up, smoke damage, etc added up to $50,000.

Those rules include having to use a disclaimer that is a bit like the surgeon generals warning on cigarettes - and if you follow the rules and include the warning, most have found that they get almost zero response.

He charged us $85 at one time to change batteries in 4 smoke detectors.

Smoke detectors. 

Holy smokes that's a good trick for DIYers, Steve.

It is a radioactive, colorless, odorless, tasteless noble gas.WikipediaSymbol: RnAtomic number: 86Electron configuration: [Xe] 4f145d106s26p6Did you know: While other estimates might be higher or lower, there is general agreement that radon exposure is the second leading cause of lung cancer after active smoking and the leading cause among non-smokers. nih.gov..    

Both properties are run-down and have long-term tenants who do whatever they want (unauthorized pets, subletting, building unauthorized structure, smoking, etc).

Days after the inspection, the buyer and his agent came by the house (based on notification from the keybox), and did their own walk through and responded back saying that the smoke detectors were not working and the electrical panel needs major work. 

They also require a roof, chimney and furnace inspection which my inspector told me all were in great condition.Other things needed are fire extinguisher and an additional smoke and co detector.

It's also acceptable to hold tenants accountable for consumables like light bulbs, smoke detector batteries, or filters in the refrigerator.