I cancelled a policy to months before. I just had to tell them in writing that the vehicle hadn't been on the road during that time. Surprised the hell out of me when that was allowed (it was actually suggested by ins company).Well, yes.....certainly retroactively to the moment before any recent major claims, that's for sure.
The insurance will be worth the paper it's printed on, and that's about it.
Thing is....people renting from outfits like this running out of some guys driveway probably often don't understand the risks.
In the case of kijiji rentals, insurance company could probably do a little research and cancel back to the oldest ad they can come up with. Just in case somebody else pops up that claims they previously hurt themselves (or were hurt by the bike).