I'm going to ignore the recommendation to stop smoking because I know a relative that has been smoking for 80 years and he's the healthiest person I know!

So my 1st booking.com guest left my home in a mess, smoked in the property and left an iron mark on my rug. 

Lighter, smokes, cell phone, lawn chair - a regular rec room, with the other tenants property as their table.

Change smoke detector batteries, new thermostat battery, replace furnace filter, look under all sinks, drain water heater once every year, look in the attic.

I make sure led lightbulbs are in all fixtures and smoke detectors have active batteries.

Is it smoke, dead rat, urine?

Over and above that you have Toronto and Vancouver which are playing their own game these days.You are far enough removed from the Big Smoke in Peterborough that prices should be moderated somewhat; the converse is that rents will also be somewhat moderated.  

Smoke detectors, GFCI outlets, handrails, working heat and hot water, etc.

Urine, smoke (whichever type) and any other organic compound has to outgas no matter what.

Sometimes a deal can be slightly negative because you're living there as a house hack now that is a different story because you might "know," that when you move out it will be positive or positive after you raise rents and move out (lets say its a fourplex 4 flat for Chicago folks, and 4plex for us west coasters).In this case, it might be lucrative because in this example you control the "move/out," and conversion from negative cashflow to a positive cashflow scenario so the future potential is definitive versus some hope and prayer that you will someday cashflow (smoking hopeium so to speak).I've also seen some buy negatively cashflow properties here in Seattle PNW (pacific northwest) areas even after they move out (its still negatively cashflowing), but the aim was to build ADU or accessory dewelling units in the back and that eventual exit strategy would yield positive cashflow eventually.