One peculiar thing about dell is how tightly controlled system they have, seemingly this part tag or system/service tag, whatever it is called is tightly integrated to their invoice and user info, and usually on Grey market items, you won't find this tag, and even if you do, it will be registered to some third party usually, and this is how they quickly determine how the product is purchased(call to Dell service assistant line, they will ask for service tag before and invoice afterwards);Case 1: I brought a Dell Ultrasharp monitor from a Dell authorized seller, and dead pixel appeared on it after two years(they have three year warranty), armed with usual Indian instinct, I contacted the seller first, and he registered the complaint on my behalf; what happened next was that I received a call from Dell about service tag, and to my amusement, I couldn't find it anywhere on the monitor, contacted my seller again and he told me to give them serial number, and so I did, and the whole process was quite frustrating because they were so persistent on that tag, and just told me to check it everywhere, dismantle the monitor from stand, check it there and all, and I still couldn't find it, and in the end, he agreed to change the piece; admitting that there were few batches without tags..(imagine my expression then); Lesson learned, Dell want total control over what is sold and will not hesitate from harassing if not purchased directly from them. Second incident; From the same seller, I purchased my HP notebook, everything went fine, and one day, to my amusement I checked the warranty period of my laptop and without any surprises, it was from the day I purchased the laptop, the laptop maybe registered itself. Now I had some problem regarding the battery, so I contacted HP on it, and during the call they just asked serial number, and registered a case on the local service center, done. Both things were purchased from same seller, and he was authorized to sell both; in one case there was this mental torture to find tag, and in other case, everything went pretty smoothly.(there were other encounters too, and I was never disappointed by HP service).
The way HP treats service request and ownership is quite different from the way Dell treat ownership and requests(atleast in India). HP will just ask for invoice in worst case, and if that invoice is from a genuine dealer, then whether the product is brought online or locally, it won't matter, on the contrary, Dell will be quick to point that it is purchased from somewhere else and so on.
I don't know about Lenovo or other dealers as of now, but I guess they follow same pattern as HP.