There are many listings for new/barealy used Sky+HD boxes on Ebay. Beware purchasing them or have the problems I've had. When subscribing to Sky the minimum contract is 12 months. You typically pay for installation and a subscription, paid monthly, for the minimum of 12 months. Basically you are buying the box for this 12 months. If you breach the contract and stop paying before the 12 months are up, then Sky can seek up to the full balance of subscription you signed up for and recover the Sky box. The important thing is UNTIL THE FIRST 12 MONTHS ARE COMPLETED THE SKY BOX IS THE PROPERTY OF SKY, YOU DO NOT OWN IT.
Now for the technical bit. When Sky first launched they the victim of extensive piracy of their encryption cards. To solve this when they went digital they set up a system which tied the individual Sky viewing card to a specific Sky box. If you plug your viweing card into your neighbour's, brother's, dad's or whoever's box it will not work. This pairing takes place during installation when the installer rings sky, calls up the system setting on the Sky box and provides Sky with the software version number, serial number of the box and the viweing card number. The computer sever at Sky links this information together and generates a clever, constantly changing algorythm using these numbers. This is then sent to the box at the same times as the programmes in the satellite signal. The box then decodes this algorythm and compares the serial numbers to each other. If they don't match the viewing card information then the encrypted channels are not displayed and th escreen tells you to ring Sky. This is what's known in the trade as an ECM (electronic counter measure). An important consequence to this is that Sky know the serial numbers of all their boxes and where they should be (based upon the account holding the viewing card).
Now the tricky bit about buying a used box. At the moment Sky are supplying receiver boxes to customers who upgrade or change their subscription (to HD for example), new customers and multiroom users. To quote my contact at Sky, you pay typically £15 shipping and receive a new £300 Sky box. What then happens is that the customer cancels their subscription and stops the direct debit at the bank. The Sky box then finds its way onto Ebay for about £100. This makes the vendor £85.
The problems start when the buyer tries to install the box. After plugging everything in and inserting their viewing card you call Sky to pair the box and the card. This initially goes through and Sky explain it can take up to 4 hours for the pairing to be confirmed. In reality its usually a lot quicker. The box appears to work until the recording facility starts to act up. Only the free to air channels will record and live pause. None of th eSky channels will pause or record. You ring Sky to fix the problem only to be told the routine installation has failed and that they need to look into why. After ten minutes (you either wait or they call you back - Sky call you back, this is serious !) they inform you that the box you have is keyed and already matched to an existing account/card. Since the account has not run its 12 months and expired the box cannot be unpaired, even though you are a legitimate Sky subscriber. For security reasons they cannot divulge details of the other account, but will confirm to you that the other account hasn't met its conclusion or payment life as agreed. Furthermore the box cannot be'un-paired' and now for the real kick in the teeth - because contractual requirements were not met, the box is still the property of Sky. Yes they are fully aware people are ordering nice expensive Sky boxes with no intention of paying beyond the £15 delivery cost and then selling them on at a tidy profit at their expence. Because they are not idiots the serial numbers of these boxes are logged on the Sky server in addition to the account/card it should be using. You buy one of these boxes on Ebay nad you are left with a box that won't work, that actually belongs to Sky and yes, they want it back.