When toner sales men ship you a crate of toner cartridges you didn't ask for, and then sends you a bill for those toner cartridges, you don't have to send them back, and you don't have to pay for them either. Welcome to the real world.
http://www.snopes.com/crime/fraud/supplies.aspThat's only because the law explicitly allows for this, as a way to prevent unscrupulous scammers from sending you things on purpose just to compel you to buy them. It's a notable exception to prevent abuse of the mail for fraud.
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.