If toner salesmen park a truck full of toner cartridges in your driveway, you don't suddenly own their truck and their toner, as the exception no longer applies.
Anything on my property belongs to me and I'd like to see them try to get it back.
You could reasonably anticipate legal trouble trying to assert that position, but of course I doubt you really mean it. Have you ever called a plumber or a repairman or had friends over? And then asserted ownership of their vehicles because they were on your property? I didn't think so.