By buying one of those cheap cable-line “filters” sold on eBay, you might think you're being clever. — However, the cable box itself has memory of any and all of its purchases, and so apparently you're most likely going to have to pay for them anyway… if the filter even works in the first place:
There are TONS of ads for these “digital descramblers”. They are NOTHING MORE THAN A HIGH PASS FILTER! They do not work!
What these things do is prevent a cable modem or digital cable box from talking back to the cable company, therefore it will not report Pay-Per-View purchases back to the cable company. Here's the catch though: The cable company is constantly polling the digital box for signal levels, purchases, and troubleshooting information. If it doesn't hear back from the box, they will flag your account and roll a service call truck on it. Since there is no way for you to clear the PPV purchases out of the boxes' memory, you're going to end up getting charged someday anyway.
Don't waste your money. (Source)
… I've seen ads for these things, which probably cost just pennies to make or obtain in bulk and can be sold for at least a few dollars each (if not more), so I'm glad that someone has taken the effort to clear this up. — Just spreading the word here, myself. 👍🏻
For what it's worth, though, on Comcast's Motorola DVR units there is a way to clear the box's memory and reset seemingly everything, but I'm not sure if it does actually clear out the PPV purchase history, as well. Beware that this will erase all of your recordings, as a minimum! — If you want to try it, first enter “Diagnostics” mode (by turning off the box and then immediately pressing the “Select” button), and then press these buttons in order: Replay, Replay, Replay, My DVR, My DVR, My DVR, Live, Live, Live.