Old clothing and shoes.  

They didn't pay and left the place a mess, with plenty of belongings like beds, clothes, bikes, etc. 

There were socks and shoes scattered on the floor, the laundry hampers are full of dirty clothes.

Maybe I need my cleaner to light up outside, walk in with smokey clothes, and see if that sets it off.

Use a "tack" cloth between.

There was roughly 3 feet of clothes, trash, etc. piled in the entire house when we purchased it.

For example:General-Filters (furnace, air conditioning, oven exhaust, refrigerator, and water)-Stove burner when the “eye” needs simple replacement-Batteries and remotes that service the premises-Fan and light pull strings-Smoke and carbon alarms testing and batteries-Ensuring appliances are properly plugged in, hooked up, and used-Removing dirt, debris, and lint in and from connection pipes (e.g. clothes dryer)-Tighten loose screws on all home functions (e.g. doors, hinges, handles, socket -Balancing off-balance appliances-Cable, internet, and phone jacks-Fire extinguishers-Systems operation (e.g. security, irrigation, HVAC)HVAC-Monthly A/C filter and drain line maintenance Electrical-Reset “tripped” GFI breakers-Light bulbs (throughout and at the end of the tenancy)-Blown fuses-Reset breakers in the outside and inside breaker boxes-Socket and plug outlet coversPlumbing-Unclog drains or toilets-Caulking around tubs and showers as needed-Gas pilot lighting-Leaky faucets and shower heads-Toilet flappers, handles, seats and seat lids, tank lid, and flush kit-Sink and tub stoppers-If septic tank present, use RID-X as directed on consumer box-Proper cleaning of garbage disposal-Loose faucets and sprayer heads and hoses-Faucet filters (i.e. aerator)-Open exterior plumbing clean out when necessary (e.g. sewage backup)Exterior-Routine lawn (and pool) maintenance-Adjusting sprinkler heads as necessary-On the last month of tenancy, tenant must perform required lawn maintenance no sooner than 2 days prior to vacate dateThere’s a lot to consider as a landlord.

Instead, they miss the cloth or aluminum wiring and poor circuit allocation and instead show you with their fancy plug that "polarity is reversed"; or the always arbitrary "the roof likely only has 5 more years left max" because they see a 3-tab shingle from the ground and completely miss hail/wind damage on a newer architectural shingle citing its "lifetime warranty".

I'm sure when you get there to do your inspection you'll find that he left his keys on the kitchen counter, took most of his clothes and left behind nothing but trash and old furniture.

Normal home owners insurance covers the house, liability, a bunch of miscellaneous items, and all your stuff (furniture, clothing, appliances, etc etc).