The customer has the right to return a perfectly working device within a few days of purchase because he changed his mind. Since the Crucial is not compatible with his computer he doesn't have to prove it is faulty to return it. He can say he changed his mind and wants another brand. About firmware updates, yes the company officially released a new version to fix bugs or improve a feature and will say nothing if you upgrade yourself, PROVIDED the upgrade is successful. If anything goes wrong or even if the device is incompatible with your system, 99% they will blame it on the firmware and may refuse the replacement claiming it is perfectly OK (NFF, No Fault Found case). In case the device is faulty there are certain companies that would claim the firmware was improperly upgraded and Void the Warranty. Are you willing to take those risks? Never attempt to fix a faulty device under Warranty, including upgrading the firmware. Just return it to the shop and let them take responsibility of any firmware upgrade.
Again, where's your proof that the drive is faulty? AFAIK the OP hasn't even looked at the S.M.A.R.T. information yet. Let alone used the Device Self-Test option in Storage Executive. Damage inflicted on a product due to improper use of the product is always covered by law. Again, nothing is wrong with choosing to upgrade the firmware per Crucial's official instructions
after you saw no S.M.A.R.T. errors in Storage Executive and the Device Self-Test also went OK. It is determined by
law that doing this does
not meet the criteria of "improper use". Sure, any company can break the law. Until they get caught. And besides, today's social media will eat their reputation if they reject the RMA. For reasons that should be completely obvious, if the drive is reporting S.M.A.R.T. errors or if it fails the Device Self-Test, then deciding to upgrade the firmware gets you nowhere. Where did you see me claim the opposite?
My point is also that you don't know that the firmware upgrade mechanism of the drive is faulty until you tried to use that mechanism to upgrade the firmware. Personally, I, prefer to find out that it is faulty
before the warranty runs out so, I always test it, as I also prefer not to use a drive that I haven't tested to some degree to store the kind of data that, were it to be lost, would likely present a bit of an inconvenience. Similarly, I also prefer not to put such data on a drive when I already know that the drive's firmware has an elevated risk of it being unstable in such a way that I can likely avoid being unstable. (Even, if this means that it takes some affort to avoid, as I will be the first to admit that upgrading the firmware of the Crucial MX500 is a bit of a royal pain, but then, that also is part why I never decided to get a Crucial MX500, anyway in the first place, so... lol
)