5 surprising iPhone issues that Apple will fix in or out of warranty, as per repair guidelines leak
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The document is dated March 3, so it includes the newest iPhones, and will probably remain in force for the ones about to be announced next week as well. Check out five surprising defects for which Apple will grant repair in and out of warranty in the slides above.
As for when will you be denied service at all, well, the circumstances must have been pretty harsh to reach to these stages below, after which you will just be served the "Return the device to user" guideline with a Genius genuine smile:

source: BI & Apple Support
Things that are NOT allowed: