Dave Meck mentions the many times he's gotten free cable through some happenstance. The same has happened to me before. At one point, I had lived in three different apartments in a row where the following sequence of events happened: 1) I purchase basic cable. 2) The cable goes out. 3) I call for repairs. 4) After the repair guy leaves, I now am getting expanded basic (several dozen more channels) but am never charged for anything but basic. I just figured that some cable guys enjoyed giving away free expanded basic when they were called out on repair jobs.
Here's what bothered me, though. Was it dishonest or unethical for me not to call the cable company back and inform them that they were giving me too many channels? I really don't know. On one hand, I was getting something that I didn't pay for. I wouldn't feel comfortable walking out of a store with, say, an extra pair of jeans just because the sales clerk accidentally put them in my bag.
On the other hand, cable service is essentially a zero marginal cost service. The electrical signals for expanded basic were already sitting right there in the cable running to my apartment, and once the cable guy had flipped the wrong switch, it cost the cable company literally nothing for me to be getting expanded basic as opposed to basic. In fact, it probably would have cost the cable company more to come back out to the apartment and flip the switch back to basic. So by not calling the cable company, I was actually doing them a favor, right?