The three main things to ask of any possible suppliers are:
1. What is the source of the units?
2. Are both the warranty seals on the unit intact?
3. Does it come with a genuine original VW code card (and manual)?
It's likely that most of the Ebay units will not have intact seals because they have been opened to read the PIN code. Hence they will also probably not have genuine code cards, regardless of how genuine they might look.
This does not necessarily mean these units have been stolen from vehicles - although be aware that they might be. There are other, legit, sources where this process might be necessary e.g units properly recovered from insurance write-offs. In theory legit refurbs should be resealed but I have seen one that I know was a refurb but did not have both seals intact.
There has been some talk in the past on many forums of units failing to accept firmware upgrades properly once the seals have been broken, because the PIN recovery involves a little soldering. I doubt that simply reading the PIN code would cause this problem (won't go into details here). But if the PIN code has been changed using this method then potentially it could cause problems with a firmware upgrade. So it's probably best to avoid units with PIN codes like "0000" and "1234", but bear in mind that just because the PIN code is a random set of numbers, that is no guarantee that the PIN code has not been rewritten.
There are other factors that can cloud the issue with firmware upgrades - for example some firmware upgrades are version specific. There are internal differences between A, B and C units (and two different manufacturers as well as different revisions of the circuit boards), and a further complication is that it is possible to apply a firmware upgrade for a B unit to an A unit and it then thinks it's a B unit, even though it isn't really. If you then apply a firmware upgrade that is intended for B & C units, you can see how the outcome might be unpredictable. There is virtually no checking during the firmware upgrade process itself, which doesn't help.
Another tip when looking at these units is that the screens are pretty tough - they don't seem to scratch easily in normal use and a quick wipe with a soft cloth gets them looking pretty good. However the black piano effect surrounding the screen is a real scratch magnet and it's worth checking this closely, especially around the two control knobs. If you are the careful type you can mask off the screen and the matt areas of the front panel and use a little Displex to polish the piano black part. If you are not the careful type then do not do this. It will go wrong and either your screen or the matt finish will be permanently damaged.
Sorry, gone a bit off-topic and had an RNS-510 brain dump instead
The upshot of all this is that you pay your money and take your chances. The people that brought units off Darren have given some very positive feedback so it sounds like he has a source of quality units. There are some dodgy units around on Ebay, but there will also be some legit sellers. There is no magic way of telling unfortunately, and of course just because someone charges more there is no guarantee that their sources are any better than something you could pick up on Ebay and get a local specialist to fit for you for less money.
If, for an extra £350 you get a unit in a nice new box, with intact seals and a genuine code card, and they install it without snapping any of the lugs off the dashboard trim and they code it correctly and don't scratch the top of your AC controls then it may well be worth the extra money - unfortunately only you can decide whether that is good value for you..... whichever route you choose I hope you take the plunge as they are great OEM units and well worth having
Cheers, Mark.
