Hi Tim, it can be a bit hit or miss with grey market Extreme devices. Typically we don't recommend buying from third party sellers, most of our warranties only apply to the original owner of a device so if anything goes wrong with the equipment you pick up second hand it can be very difficult to get support for the device at that point. You also run the risk of the AP being still registered to the old inventory, and then you'll need to start this whole process with me to get it released which can take a while as you can see. So there is a bit of risk involved in purchasing our devices second hand, but I will always do my best to assist in these situations.
I think it's an excellent idea to check with me before buying third party devices, so I can tell you if there is still a previous registration for that device. For instance, I can tell you there are no previous records for 01301505120112, so were you to buy that device you would be able to add it to your inventory without my help.
Hope that helps!