That's something to be dealt with with the seller of the original second hand product.
In my jurisdiction there's the concept of a "hidden defect" at purchase, but what happened here is a bit different because the back was in the posession of the purchaser for a longer time (1 month without use) so I guess the lines blur then a bit as you cannot "prove" 100% that the problem didn't arise during the owneship period after the purchase.
I am just saying in the grand scheme of things this can happen if you buy second hand at a big discount and out of warranty product without seller's warranty. Its a risk you take to avoid paying full price. So in a way its IMHO difficult to get entitled and "pissed" about a 2nd hand purchase to get in on the IQ4 action for cheaper. That the flip side of the coin when buying used ... it is USED and OLDER than NEW.
I recently sold an old scanner (IQSmart 2) and made it very clear to the purchaser that if something happens tomorrow it is his risk. He got a good price for it and understood the risks and still went through with it. There's never a guarantee with electronics after some years, but this being said, the IQ4 is a rock solid product and I guess it also depends on the specific unit and how much "outside" and "heavy" use it got which could have affected the internals somehow.
My understanding here in the US is there are express and implied warranties with products sold and that's governed by the Uniform Commercial Code. Unfortunately for us, warranties are not infinite in duration. By law in the US at least, P1 will go by the book because the transferable warranty expired and the buyer was never in "privity of contract" with P1. So P1 is not going to feel they owe a duty on a product out of warranty that was purchased by someone they were never in privity of contract with. They sold it to an original buyer who is not the current owner, the warranty expired (which is a generous 5 years, even more so because it's transferable), and they are going to feel they owe nothing more to the current end user since it would be a loss on their books. We get emotional about this stuff because of the cost and attachment we have to our gear, but I don't anyone can fault P1 for this standard business practice.
Purchasing from a dealer (i.e., a merchant who deals in the types of goods sold under the UCC), they may provide their own warranties, and it's great (for us) to hear that CI and
@Steve Hendrix have flexibility and are not so "by the book." I believe used backs purchased from CI come with a CI warranty but Steve can chime in more on CI's policy if he wishes (or any potential purchaser can just reach out). It really stinks that OP's dealers in China didn't stand by it, but that's their perogative I guess, and Chinese law is diff than here in the US.
Anyone can feel free to correct me if I'm mistaken. I'm currently studying for the US Attorney Bar Exam that I take tomorrow, so I hope my understanding is correct at this point in time
$3500 repair for OP's back sucks but it's better than $15k or having an expensive paperweight. At the end of the day, we all must remember there's an inherent risk in buying things second hand, and warranties are not infinite in duration. On the other side though, the "quid pro quo" for our assumption of the risk is that most of us are looking to purchase a back at $20k or less, which is a lot cheaper than the $45k or so list. So assuming OP's back comes back great at $3500 repair cost, that's still cheaper than a new one.
I once had a navigation system on a car die on me one week out of the warranty. Best the dealer and manufacturer could do is offer me a rebuilt unit at half the cost of the new one (1800 vs 3600). It wasn't free, but it was better than the cost of a new one. Unfortunately these things happen.
Hopefully OP gets his back fixed and gets much continued use out of the back (and please share some results with us!).
